We haven't gotten to the Fast Attack section of the Dark Eldar review yet so I thought I'd chuck these two units up as a comparison post. Why? They seem similar but are not and both play a very vital role in Dark Eldar armies. The majority of Dark Eldar anti-tank comes from S8 AP2 lance weapons. Whether it's the long ranged Dark Lances or shorter-ranged Blasters and Blast Pistols, there is very little firepower outside of this statline. Both Scourges and Reavers bring to the table one of the weapons which is importantly different from the darklight weaponry and are both on fast platforms in the Fast Attack slot. Ergo the similarities. This weapon is the heat lance which brings melta status (and lance) + AP1. This is very important for breaking vehicles. Whilst 20+ S8 lance shots is going to cause quite a bit of damage and suppression to vehicles, they are not reliably going to bust open tanks (you need 27 Darklight shots to drop 3 AV11 tanks on average, assuming no cover). This is where AP1 comes in which is easiest to get for Dark Eldar in the Fast Attack slot with Reavers or Scourges (Talos in Heavy Support can also take heat lances and Harlequins in Elites can have Fusion pistols). AP1 gives you that bit of extra oomph and reliability against armor and the melta status helps ensure those shots are getting through. So let's get down and dirty with both units.
We've covered how they are similar (fast platforms with melta options) now let's cover how they are different. We'll start with the Reavers.
Reaver Jetbikes
The first thing we notice is we are getting one special weapon per three models. This means at certain model counts the Reavers have access to more weapons (i.e. three and nine models) but need an extra model (six total) to access the second special weapon and have a lower ceiling compared to Scourges. Reavers only have two weapon options however, heat lances and blasters. As mentioned before with the saturation of darklight weaponry elsewhere in the Dark Eldar army, heat lances are really the weapon of choice for Reavers here.
Reavers are also more mobile than Scourges thanks to their Jetbike status and combined with skilled rider, this makes them vastly more survivable as they can enter terrain reliably and get a 3+ turbo-boost save. Combined with the 6" assault move in any direction and Jetbikes can blow up a tank or infantry unit and hop out of harms way (to an extent at least). Add in the extra mobility with the 36" turbo-boost and Reaver heat lances are going to be in your opponent's face from Turn 1. Make sure you protect them behind cover if you aren't going first though. This 36" move is also capable of doing damage to opponents thanks to Bladevanes and upgrades like Grav-talons and Cluster caltrops. Whilst not a huge amount of damage, being able to go extremely fast and damage a single unit is an excellent bonus to have.
Furthermore, Reavers are much more combat capable than Scourges. Reavers come with two close combat weapons for +1A and also have I6 compared to I5 on the Scourges. Having 3A on the charge plus combat drugs and effective T4, Reavers aren't too shabby in combat considering the units they will be engaging are generally backfield units. This adds some excellent utility and means they aren't completely useless against all foot lists. That being said they only have a 5+ save in combat so without a pain token they are pretty vulnerable.
Scourges
Scourges have two main differences compared to Reavers. They have a 4+ save standard (so don't die to boltguns if caught in the open) and they have a lot more weapon options. Scourges are able to access two of these weapons for every five models so are better at getting double special weapons and have a higher ceiling than Reavers. Although the 4+ save is better than the Reavers 5+, the lack of turbo-boosting and ability to enter cover reliably actually makes them weaker in defenses. However, the 4+ means the Scourges aren't dying to AP5 weapons if they need to go into the open to drop tanks. This is especially important if they deep-strike.
Whilst Reavers are more mobile due to their Jetbikes, Scourges are capable of deep-striking. This can work very well in a Duke list without a webway portal as they are able to significantly affect the game the turn they come in (rather than zooming on from the board edge). Even in more normal lists, the deep-strike option gives them a bit more flexibility in placement compared to Reavers coming on from the board edge. Outside of this however, Reavers are generally going to be a better option for a heat lance delivery system (unless you're really tight on points). However, Scourges have access to a much greater variety of weapons such as splinter cannons, dark lances, and haywire blasters. All of these are ranged weapons where the Scourges are better able to protect themselves (cover) and still remain effective. Splinter cannons and haywire blasters are particularly good on Scourges as they can move and shoot (unlike Dark Lances) and provide excellent anti-infantry or suppression fire.
Scourges also come with better standard anti-infantry guns and have a higher ceiling in terms of anti-infantry potential. Although Reavers are able to affect infantry with their Bladevanes and in combat, Scourges come with shardcarbines and when combined with weapons such as splinter cannons, can put out a lot of poisoned shots at range and put a lot of pressure on infantry.
Summary
Reavers are generally going to be the better delivery system for heat lances. Although a tad more expensive due to needing six models to access the second special weapon, the increased mobility, survivability, ability to go into terrain more reliably and combat potential makes them much better at harassing an opponent's backline and damaging infantry and tanks alike. Whilst Scourges can be used as heat lance delivery systems, particularly in reserve based armies without a Webway Portal, their greater access to special weapons such as haywire blasters makes them an effective ranged infantry support option.
