I have to say, largely on nostalgia, I think the Stunticons are my favorite combiner team. Despite having the silliest name, the least convincing backstory, and a leader figure that makes the limbs look small enough to be digits, I have always just loved their overall aesthetic. They're basically a nihilistic group of disturbed, pissed off thugs who are muscle cars and a tough ass truck. They're sort of the outcast outlaws of the Decepticons. For my least favorite, I have to admit I thought the Predacons were kinda lame. But that's just because I've never been one to care for beasty altmodes.