That is a very controversial question...
4wd is easier to drive on a track - just point and shoot (and braking is also easier with 4 wheels, not 2)
With 2wd, steering and managing power is harder, but the drivetrain is easier to maintain and there are less moving parts that could break. Traction is also a problem but that only bothers hardcore racers.
- IMO, 2wd has more of a fun-factor, with quick touch-and-go turns and fun donuts

You can make the choice (most nitro buggies and truggies are 4wd... stadium trucks are almost always 2wd)