For me, I don't count Zartan, Gold Destro, or Serpentor. To me their vehicles were more like big accessories. But feel free to mention them if they are your favorite.
For my money, the best figure to come with a vehicle is Steam-Roller. The dude had a crazy six pack and a tatoo. My Steam-Roller's arm broke off at the bicep at one point, but that only made him more of a badass in my Joe world. Definetly an underrated figure.
So who's your favorite vehicle driver?