Magneto, Doom and other majestic figures are probably the obvious choices. But i go with the Green Goblin. He is, in my opinion, the greatest of Marvels Supervillains. In a very comic booky way he is even more complex. He works as a lunatic in a Halloween costume as good as mad scientiest in a labcoat or as a manipulative bastard in business suit. He works on a street level basis as good as on the top of an Evil Empire. Norman Osborn is Lex Luthor and the Joker in one person.