I own GP3.5, Reflex and Phoneix for sims along with lots planks and a couple of T-Rex 450 V2's. The Phoneix has a TRex baked in and it flys pretty realisticly.
[link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXPNM8&P=7[/link]
The GP sim heli's are on rails but they do have good tutorial info and practice sessions. With GP 4.0 coming out, I would tend to take a trip to the LHS and play with it a bit. The thing I don;t like is the GP sim doesn't have anything other than Hobbico planes/helis etc. i.e. my TRex is not baked in and I have not found one to install that is really good. Hence for the TRex 450 and 600 fliers, phoneix is the way to go.