Some one correct me if I'm wrong but choosing servos is basicly all about how much torque and speed you need. This:[link=http://www.csd.net/~cgadd/eflight/calcs_servo.htm]Torque calc[/link] should give you a pretty good idea of how much torque a planes servo needs.

Speed on the other hand... Basicly, the faster the better, especialy for 3D.