SimfPhys - the most car-base addon. It has a lot of good functions. Now i made my own cars, only for the headlight system I respect it wholeheartedly (ITS TOO COOL). Then, good physic, the best wheel system. And a lot of our customization (for ex. you can add changing bodygroup of model on while you turning headlights(it's withoutadditional third-party scripts, it's base functions of SimfPhys))