I really don't like the Attack Helicopter, sometimes it works reasonably well but more often than not it just hovers around above peoples heads doing nothing and its very easy to escape if you become its target.
Chopper Gunner has to be my fav, I manage to get it most games and its just alot of fun to use.
Current setup:
Counter Spy Plane(mainly because a friend of mine uses the Spy Plane alot so its nice to have them stack up and everytime he uses one POW! spy plane denied :D
Mortars(i seem to be good at guessing where people are with these)
Chopper Gunner
I'm thinking about getting dogs soon though as I'm over half way to my next prestige and havn't used them at all yet.