Are people really sleeping on Fedor? The dude massacred Nog on the ground from within his guard and took it to Cro Cop on the feet. He could knock you out on the feet, he could take you down at will, and he could tap you in seconds. And even within each discipline, he was incredibly comprehensive, from his punches and kicks in his striking game to his trips, throws, and slams in his TD game to his chokes, arm locks, and leg locks in his submission game.
I think that the level at which he could do literally everything puts Mighty Mouse in the #1 slot, but Fedor is right behind him at #2 in my book.