It depends on the size of the track you will run on, the traction on the track, and the class you will run. In a 2wd buggy on a small to midsize track alot of racers are using 13.5 motors, with timing advanced. If the track is a little larger I would go with a 10.5 motor. Dont forget that with the tunability of these speed controls, either setup can be crazy fast. Try a vtrax10 with either one of those motors.