Since I am a little bit of a weight weenie (a totally unecessary addiction in my case) I got a couple of FOX air shocks (F80 and F100 RLC's).
They are great shocks and perfect for what I use them for, but I wanted to get coil shocks for 2 reasons.
1) reliability, they are pretty bullet proof, and simpler than air shocks.
2) They have a more "buttery" feel/action, but they are heavier. Seems like 5+lbs as compared to 3+lbs.
I think a 100mm would work fine for you since you are mostly doing trail (and it sounds like your bikes geometry is probably built ro 80-100mm shocks).
As far as all the U-turn/comp/rebound damping etc etc etc, I find the simpler the more reliable.