I haven't really been following a discussion on the Eldar tactica thread regarding Falcons and their uses but I chimed in with some more appropriate stats and my 2 cents and thought I would expand on it here.
Firstly the post in question is here. I'm sure you can't miss it at the top of the page.
To summarise and expand on what I said.
First and foremost. HF can work on Falcons because they have multiple guns and losing one doesn't cripple it's effectiveness. HF make a result of 1-3 much more likely and combined with stones leads the Falcon to be shaken or lose a weapon. Combined with the fact wherein keeping the Falcon alive keeps a scoring unit happy is a price I'm willing to pay. The Fire Prism on the other hand does not want to lose weapons and paying the extra points for it is not worth it. If it dies, it dies. Move on.
Holofields are at their most efficient when AP1 is not a factor and serpents are marginally better through raw numbers at surviving melta shots at close range.
In direct relation to Fire Dragons, they are better off mounting up in Serpents to allow Falcons to stay at a longer range to avoid AP1 mitigating factors (as new books come out this may become obsolete as more armies gain access to long ranged AP1 weapons).
Whilst Falcons w/HF aren't hugely worse at sucking up meltashots at close range, you've paid through your teeth for those HFs and thereby taking a more expensive tank to do what a less expensive tank can do at a marginally better ratio is just plain inefficient. Falcons at range w/HF are a pain to kill. Depending on BS, cover, SMF, strength of opposing weapon and fortune the Falcon's raw death percentage can vary from 7% to 0.6% . To waste this by sending it into the teeth of the enemy is a waste of the HF points. Either use serpents to drop off Dragons or don't buy the HF and accept it will most likely die when it drops off the Dragons.
In terms of comparing its survivability to 5th edition (excluding AP1 and -), it hasn't changed. No longer do skimmers auto wreck on an Immob and a Penetrating hit now has a 1/3 chance of destroying the skimmer. In 4th edition the combination of Skimmers = wreck on Immobs + glancing only also created a 1/3 chance of destruction. On the other hand, every other tank in the game became stronger. Still, few books have tanks which can utilise a defensive upgrade as well as the Falcon and HF (disruption pods come to mind). On the flip side, 5th edition did downgrade the Falcon's offensive prowess and mobility. No longer can it move 12" and fire all of it's weapons S6 and below and is therefore relegated to a 6" move if it wants to fire at full efficiency. With the increase of melta (thereby pushing Falcons to a more mid and backfield game) and increase in DAVUs, this is less of an issue.
In my warseer post I covered essentially its most basic uses as a firebase (mitigated or not by a Farseer) and using cheap Avengers to make it scoring and we covered again here its excellent defenses. So what now? We know from raw stats the Falcon is more survivable against ranged weapons which don't get an extra die for penetration and our very valuable and short-ranged Dragons are in Serpents. Use it as a first turn screen when not facing an army where the Serpents are better off in front. This opens up a lot more avenues of approach for Turn 2, particularly if you advance within range of an objective (an immob result on the Falcon doesn't leave you stranded). From that point onwards when meltas begin to get in range the Serpents can take over and the Falcon can still screen the Prisms (if you have any).
There seemed to be three camps online. Don't use Falcons as they now suck (huh?) or use them (split into two camps with DAVU on one hand and Dragons on the other). In terms of efficiency I can not really see why you would want to put Dragons in a more expensive tank (even w/o HF). If you don't want to use Falcons and run 3 Prisms, go ahead but I think in terms of scoring efficiency you are losing out.
This sort of meandered out without a point hmm. Anyways, don't pay through the nose on your Falcon only to bumrush it towards meltaguns and bitch when it gets slagged.