Obv Jim Starlin with Thanos.
Then you have your Grant Morrison Batman, your Joe Casey Superman, but everything else comes a distant second by comparison.
A rather obscure example of wankery is Christopher Priest with The Immortal Iron Fist. He wrote a truely OP Danny, having him cold clock Cage with no effort, shred Black Panther in his Vibranium suit, and even KO a character who manhandled Thor and She Hulk (Bres).
Priest seemed to truly enjoy writing Iron Fist, it's a shame he never got the chance to become a regular of the character (Likely pigeon holed into T'challa duties)