DF-03 is a lot tougher than DF-02 and has more race orientated upgrades available for it if you decide you want to race it, things like 2 different types of carbon chassis kits, loads of aluminium and carbon fibre bits, 1-ways, etc. The only drawbacks to the DF-03 are that it uses funny pitch pinion and spur gears (although there are ways round that) and that the motor is buried away in the rear of the car and tends to get rather hot. Plus the DF-03 based cars both have rather silly names.
-Steve