One is not intrinsically better than the other, it depends on your application and the particular details of the two transmissions you are comparing. One transmission may favor a particular dynamic event over another; for example, the 4-speed may be better for the acceleration event, but not the endurance event. So keep your design goals in mind and how you would like to perform in each event. The method for figuring out which will perform better than the other is to model the different events/situations and calculate the times. It is not an easy task to accurately model a vehicle, but you can get close, especially just starting off with an acceleration model. There are also software packages out there to help you, check out the team resources page of the formula hybrid site. There is a pretty good simulator there.