There are two transports for Dark Eldar: the Venom and Raider. Both are open-topped, AV10, fast skimmers which really limits their survivability but makes them very fast and capable of dropping off assault units which can then assault. This speed is a defining factor of the Dark Eldar army as these vehicles make up the core of any mech or hybrid list (not that the other DE vehicles are any different). The ability for all passengers to shoot from these transports can also help Dark Eldar infantry survivability whilst maintaining offensive effectiveness but obviously limits their mobility to 6”. The open-topped factor also decreases the damage Dark Eldar take during an explosion but are still likely to lose 1 model per 3 on-board. The trade-off between minimised damage done during explosions, the ability to assault after disembarking and firing all of your models when embarked and having paper-thin armor is a fine line between being too weak and balanced. It is important to therefore not expose your transports to unnecessary firepower and maximise this ability during your movement phase. One of the major relationships between Dark Eldar and their transports is they are unable to buy transports if the original unit size is larger than the transport capacity. This minimises the 1+1 concept and some flexibility when list building.
So... the Venom and Raider. Both are excellent options both are obviously best suited for different roles. The primary differences between the two can be boiled down to transport capacity, weapon load-out and upgrades allowed with the most important one being transport capacity (obviously). We will look at each transport separately and then analyse the upgrade options between them.
Venom:
The venom has the smaller transport capacity, maxing out at five-strong. This excels it towards MSU play or delivering small squads. However, Dark Eldar are very weak and are extremely vulnerable to torrenting with T3/5+. Having such small squads can often lead to easily dead squads or multiple squads breaking and running away. The Venom therefore specialises in delivering or protecting small crack squads such as Incubi, Warriors or Trueborn which are not going to rely on their numbers to truly be effective. Incubi have the survivability to not need numbers unlike Wyches/Bloodbrides whilst still maintaining their offensive effectiveness. In fact, too many Incubi can often lead them to wiping out squads or being a huge target priority for your opponent whilst smaller squads are less threatening and more likely to stay locked in combat during your opponent's turn all the while maintaining a significant offensive impact. Warrirors and Trueborn are capable of taking multiple special weapons at a small squad size (with no gains as the squad size increases) and aren’t too expensive and can thus be taken in multiples for survivability through saturation and increased fire potential. The ability for them to fire from the transport and after the transport has moved 12” for an impressive threat range of 24”-33” for Blasters makes them effective tank hunter units.
The Venom itself is also capable of being upgraded to a become a very potent anti-infantry platform with 2x splinter cannons. The two of these put out 12 shots even when the Venom moves 12” and for 10 points, this upgrade should rarely be left off. The Venom also comes with a flickerfield which is a 5++ and provides some survivability to the paper-thin nature of Dark Eldar vehicles but should not be relied upon. Particularly with the Venom's smaller profile, Venoms should be able to generate cover more readily from terrain and other objects on the table. What the 5++ safety net really provides is the ability to move into the open and still maintain some degree of fortitude.
Due to a Venom’s smaller footprint, they are also excellent choices to use in conjunction with Duke Sliscus’ vehicular deep-striking ability. This will be discussed more in his section and under retro-fire jets but suffice to say having a vehicle half the size of a Raider which can drop 12 anti-infantry shots on the drop is nice to have.
All in all, Venoms are relatively cheap considering they are effective anti-infantry platforms by themselves. However, they are not the optimal transport choice for every unit in the Dark Eldar codex. Their transport capacity of five limits their applicability as some Dark Eldar squads just aren't very good at small sizes. Although MSU is workable with Dark Eldar, be very wary of the fragility of the infantry and vehicles it composes of.
Dark Eldar Raider:
The Raider has the larger capacity of the two vehicles with ten models fitting comfortably on this pointy skiff and also only has one gun. This gun can either be a Disintegrator or Dark Lance and frankly the Dark Lance should always be chosen. The disintegrator was great in the last codex as it could fire in two modes; one of those modes has been removed and due to lots of cover, it’s current mode isn’t so hot. Whilst it can be pretty effective, other units such as Venoms or even Dark Eldar Warriors being carried by the Raider, are much better at anti-infantry. The Dark Lance however provides the Raider and whatever unit it was bought for, an extra anti-tank shot. With only one gun it’s not as versatile or durable as the Venom but should always be moving 12” unless the unit within wishes to shoot.
With increased capacity also comes increased upgrades and options. Whilst the Venom is probably the better option for crack squads in delivering lots of anti-tank close to the enemy, the Raider can also perform this function. This should generally be done when the extra Dark Lance provided by the Raider is more important than the anti-infantry firepower of the Venom. The increased transport capacity does provide the Raider with more options however. Whilst it can run as a delivery system for smaller squads and provide anti-tank fire support, the ten strong capacity of the Raider allows units like Wracks, Bloodbrides/Wyches and even larger squads of Warriors or Trueborn to be ferried around the battlefield. Certain units like Wyches and Wracks require the increased capacity the Raider provides to be effective offensive threats. Whilst both can be pretty survivable in their respective roles, their relative cheapness generally requires squads ten+ strong if going offensive. Warriors and Trueborn can also be outfitted for anti-infantry or anti-tank drive-bys much like in Venoms but with increased numbers and anti-infantry potential. This will be discussed more in their respective reviews but suffice to say the main advantage of the Raider in terms of transport capacity is a greater degree of flexibility.
Transport Uses:
Before we get into the upgrades let's look at how transports should be used. Dark Eldar transports are excellent at the 1+1 and army within an army concept. Basically, for each FoC Dark Eldar are able to generally take two very effective units in the parent unit and transport. This is obviously limited in Fast Attack and Heavy Support but Troops, Elites and HQ are all capable of taking advantage of this. With one of the main differences between Raiders and Venoms being their firepower, any unit can take either transport to add anti-infantry or anti-tank firepower to that specific FoC slot. Whilst Dark Eldar aren't pure specialists (they are what Eldar want to be), Dark Eldar transports are what really provide the army with some true duality.
Dark Eldar transports also provide many of its units with mobility. Whilst most Dark Eldar units are capable of coming through a Webway Portal, have fleet and/or move 12"+, having a fast skimmer as your transport obviously speeds things up a little bit. Add in the open-topped nature and assault units can be in your opponent's face Turn 1 (whether or not they are eating bubble-wrap or bashing up actual goodies is to be seen). Without this core mobility for many of its units, Dark Eldar would be a far less aggressive and mobile list and whilst there are some lists that won't utilise this (i.e. foot Wyches + Beastmasters), it is an important aspect to understand when building a Mech or Hybrid Dark Eldar list.
Upgrades:
Raiders and Venoms both have access to quite a few upgrades which are either five or ten points with Raiders being able to access more than Venoms. Any upgrade with an asterisk (*) is usable on the Venom as well as the Raider.
Chain-snares*: With a bunch of vehicles flying over a bunch of units this could cause a lot of damage but you'll often get more damage out of straight-up shooting or assault with appropriate units/firepower. This also often puts your Raiders in harms way and is only going to do a max of four S4 hits so isn't really worth it.
Enhanced Aethersails: The increased movement is great, even if it is random. As a bonus it's is very cheap. The lack of ability to shoot or disembark is a bit annoying but the ability to quickly re-deploy or come on up to 36" from a table edge and pressure your opponent can be worth the turn of sacrificed firepower. Combined with the ability to assault out of their transports, this can put even more pressure than normal on your opponent and this upgrade is best used on assault unit transports which are unlikely to shoot anyway. Whilst you may not always use this upgrade, it is pretty cheap and provides some nice utility when the situation arises.
Envenomed Blades: Having your vehicles in combat isn't a fantastic idea and a couple S4 hits isn't really going to scare anyone away from assaulting them (unlike say lots of flechette dischargers). Points are much better spent elsewhere even though they are cheap.
(10) Flickerfield*: This is probably the standard upgrade for Dark Eldar vehicles. Whilst moving fast or gaining actual cover will benefit you more than a 5++, there are a lot more cover ignoring weapons than invulnerable ignoring weapons and you're not relying on terrain or intervening units for cover. This gives Dark Eldar improved mobility in terms of where they can go and remain 'survivable' and is a minor balancing force relating to their paper-thin armor. Beware of Null Zone though! Furthermore, because a flickerfield provides an invulnerable save you're going to get this save when most other vehicles do not. Ramming Dark Eldar skimmers is very hard to do with a 3+ dodge, armor value and then 5++ whilst if they are doing the ramming, they automatically get a 5++ with flickerfield (assuming they can ram). Death or glory via tank shocks also gets a 5++ and even in combat, 5++. Whilst the save is lower than normal compared to other vehicle saves, you always get it. Venoms come with this standard and they are an excellent investment on all other Dark Eldar vehicles.
Grisly Trophies*: Dark Eldar don't really suffer too badly in terms of Leadership but being able to re-roll a unit's Ld test to stay in combat or an unlucky roll in the beginning of the game is a nice option to have. This upgrade could potentially 'replace' leader characters in squads as a cheaper alternative but is reliant on the transport staying alive. Considering two tests are often taken immediately after a transport dies, this can be counter-productive in terms of 'saving points.' Again limited by range however but if you have some spare points adding a couple of these to your vehicles can make your army more reliable...just don't rely on it :P.
(10) Night Shields*: Night shields are a bit hit and miss (no that was not a joke). Their most obvious role would be to reduce the range of enemy long-ranged firepower and allow you to snipe from relative safety with your long-ranged weaponry. Unfortunately the majority of Dark Eldar's long-ranged weaponry is 36" compared to 48" for other armies. However, Night Shields can force your opponent to deploy more aggressively (i.e. not deploy mech in two 'ranks') so they won't be affected by Night Shields and be caught out of range. Changing your opponent's deployment is a good thing even if it does benefit them as you are able to take advantage of that (and exposed mech is good for Dark Eldar as their lance spam can attrition vehicles down). Furthermore, due to the mobility of Dark Eldar armies, Night Shields can be used to reduce incoming firepower from spread out forces as the Dark Eldar focus on one side of the board. This should generally only give you a turn or two of reprieve but every 'missed' shot is one more vehicle potentially standing. Night Shields really shine in midfield however by reducing the range against medium to short-ranged weapons such as Impaler cannons, meltaguns and bolters. For 10 points Night Shields are pricey and although they can work in both mid and backfield, it's a lot of points to invest and how you plan on using your vehicles is an important consideration to make for this upgrade.
Torment Grenade Launchers: Reducing enemy leadership is nice; even a -1 factor can make Ld9 troops just that little bit easier to force off the board but a 6" radius is pretty small and forcing units to pass an Ld check to assault a vehicle? Meh not scary. If you have some points leftover and are running an aggressive mech style list a couple of these on some of your Raiders can essentially force your opponent to operate at -1Ld but this obviously exposes the Raiders. Would be nicer to have on Venoms who generally are more aggressive in dropping units off but is again a nice utility upgrade if you aren't strapped for points.
Retrofire Jets*: Take Duke if you want to do this, please. Deep-striking for five points is a nice option, particularly for the smaller Venom chassis. However, units are unable to disembark during this deep-strike move which forces you to be more aggressive on the drop or risk being out of range with weapons like Blasters. If you're planning on having multiple vehicles deep-strike, just go for the Duke who gives you a better deep-strike option and other army bonuses. Otherwise this option is generally much better on the Venom due to it's smaller chassis size and carrying units with multiple special weapons.
Eidt: it was pointed out to me that I forgot when you deep-strike you move at cruising speed and thus cannot shoot with the occupants. This again moves things towards the Duke who does allows this in terms of transport use though you can combine them with webway portals (agian, Duke is probably better if more expensive).
Shock Prow: Shock prows are an excellent upgrade for Raiders, particularly at five points pop. Not only does this allow the Raider to tank shock units and thus give Dark Eldar some breaking power but increases the damage a potential ram can do. Normally ramming at high speeds with open-topped AV10 vehicles is silly but even a short ram (i.e. 9") can generate a S6 hit on your opponent. Allowing Raiders to tank shock however is the important aspect here. Tank shocking essentially gives you some ability to move your opponent's models which is important for breaking through bubble wraps, pushing units off objectives, clumping units, pushing units into/out of cover or into/out of assault range, etc. Particularly important to note is that shock prows provide Raiders who have had their gun blown off with more options on how to disrupt your opponent. Not only are they movement blockers but clumpers and rammers as well.
(10) Splinter Racks: Splinter racks are both good and disappointing. The ability to re-roll BS4 poisoned shots from splinter rifles/pistols is a very nice bonus for any large Warrior squad in a Raider to have. However, this benefit does not benefit carbines or cannons who really put out the firepower in terms of number of shots. If you're running large Warrior squads in Raiders and are low on anti-infantry firepower this is a nice upgrade to make your Warriors a little bit more effective against infantry.
All in all Night Shields, Flickerfields and Shock Prows are your 'standard' upgrades which you should use extensively with Splinter Racks, Torment Grenade Launchers, Aethersails, Grisly Trophies and Retrofire jets (though seriously, use Duke) all having some decent utility and are excellent ways to spend any leftover points whilst benefiting the army.
Conclusion:
Dark Eldar mech has been heralded as too fragile but the speed and firepower it can help bring to the table fits the aggressive nature of the Dark Eldar book when required and provides extra survivability for the units held within. Whilst not all Dark Eldar armies are going to utilise or rely upon the transport options, both the Venom and Raider are staples in many lists and really help the Dark Eldar make cohesive mechanised or hybrid forces.