IMO I have had both belt and shaft driven cars and I find that belt driven has a more forgiving transmission and can take the stress of front one-way and solid. Also a little drag helps me keep the car in control without making the brakes fade when racing. Whatever it is, buy the car that your friends has and also local track support. with friends running the same type of car, you can get valuable input from them.
However, if you are planning to just bash your car in a carpark, get a shaft car.
otherwise trust me you will hate plucking stones out of the pulleys of the belt.