HobbyJapan2000.com RC, R/C Radio Controlled Planes, Helicopters, Cars, Boats, Tanks etc ... Information Center: 

1. The main points of difference between Collective Pitch & Fixed Pitch RC Helicopters

Fixed Pitch:
Easier to build & set up. Fewer moving parts.
Less Expensive.
Just a bit harder to fly than Collective Pitch.
Flying style limited to hovering indoors or outdoors and forward flight. 

Collective Pitch:
Harder to build & set up. More moving parts.
More expensive.
Easier to fly than Fixed Pitch, and more controlable
Flying unlimited either indoors (with enough space), or outdoors. For example, the Collective Pitch can do fast forward flight, loops, rolls, stall turns, inverted flying, in place flips, and any style of flying an RC Pilot is willing to develop the set up & flying skills he or she wants to.