I currently own the MVAE. Before the MVAE, I used the Advanced Escort (Prometheus). I can tell you, the MVAE is the choice for me. I like the extra firepower the other two sections bring, while still giving me my entire weapons arsenal (The other sections do not use your weapons, they have beams/torpedoes).
i fly the defiant minus the cloak. in all honesty, the cloak doesnt do much for you unless you PvP. in STF, its really not worth a console slot- and since you get an extra eng console slot that the cloak comes with, you can take it out and put in an extra eng console (i use a +18 neutronium console) to have the console layout of a fleet escort with the boff layout of the defiant.
i also use the mk xi MACO shield with the aegis engines and deflectors (not sure if anyone else uses this, but its damn good on an escort- better than the full aegis set imo). and although i dont have the math to back it up, in my sci console slots i use the mk xi biofunction monitor and it seems to do wonders for me- with a crew of only 50, crew regen is a huge factor- the biofunction seems to restore my crew at a much faster rate which in turn helps my healing abilities a ton. i dont pvp much, and when i do, it seems to help a lot there too. again, i dont have the math to back it up, but that is the least useless sci console for the defiant.
I concede that there are lots of weak mobs that can and should be dealt with by AoE but I maintain that this has to be done cautiously. Using CRF on a spawn that includes a sphere or two on elite is going to get you killed very quickly and that doesn't help anyone.
If you cant tank everything on Normal with your escort, you are doing something wrong.
As for Elite, if you have to tank Spheres, your team is doing something wrong. Each mission has a good way of avoiding tanking multiple nasties now (minus Cure, which has those Raptors to watch out for) but in any case, your team should be team-healing you on Elite anyway if you are taking most of the damage.