If Mephisto actually counts, obviously him lol, cause of his powa!!!!
For a classic villain, Sandman. Dude has great strength and power, but cause he's less smerter than Pete, he loses.
Does Juggernaut count? Cause he would be a great choice. Not only for his great strength, untoppability, and durability, but the Gem of Cytorrak in the right hands can be used for more than making you a hulking powerhouse. That's just all Juggernaut uses it for.