A military-spec Deuce and a half has got to be one of the worst. Despite 6-wheel-drive, the solid rubber tires freeze and basically turn into blocks of ice, making it all but an out-of-control freightrain on wheels. That being said, I'm sure an original VW Beetle would come pretty close to being the worst. If you were referring to cars you could go out and buy on a lot today, I'd have to say a Pagani Zonda, Gumpert Apollo, or any of the other insane RWD supercars. What do they average, like 0.5" ground clearance and track-rated slicks? Most every other 'average' car is fine in the winter with a set of snows.