Best: SMG. Hey, outer space is known for super-hot stuff. That, coupled with Mario spastically launching left and right and the overall great heat effects, it's hardly a contest.
Worst: SMS. I'd barely call it a level, really. It's just an annoying-as-heck prelude (with the same name as an alcoholic beverage--yes, I know it's Italian for "crown", but it was still kind of odd) to the final boss battle.