Well, obviously the Doctor would be a Reliant Robin that could travel in time and space. This isn't just because, you know, the Reliant Robin TARDIS is the best concept ever: it really does fit. The Doctor is a little bit odd, a little bit quirky; you just know he'd be the three-wheeled car.

I am off to Oxford in a moment, but when I get a chance to I will try to assign cars to the others. (I need time to think about them, too. It's much easier when you're dealing with people whose car preferences and the things they value in car design are made extremely clear.)