venom- because of the way he appeears and he is super powerful, sabertooth- because of his abilities and powers, rhino- because of his lack of witts and apperance, lizard- because of his apperance and powers, and iron maunger (sorry if i spelled long)- because of his giant-sized apperance.
Loki, but not just because of his looks. His character really tugs on your сердце string and he goes about his nasty villainous things with the sense that what he's doing is right and fair. His back story is interesting and emotional and Ты really feel like Ты understand and can (in a weird kind of way) relate to his actions as a villain.
But also who can resist his cheek, humor and that smile.