Tiger overpowered Carter and Fullmer, both serious candidates themselves. LaMotta has a good case as well.
carter was indeed a very powerful man at 160 and even stunned tiger late in the fight, but no one goes head on with a juggernaut like tiger and wins at 160. tiger & carter post fight: http://yfrog.com/64tigercarterj carter's face is swollen and battered while tiger looks fresh and ready to go another 10 rounds.
don't forget floro fernandez (good fight) and henry hank as well. both those guys were powerhouses at 160 themselves.
Tiger was the first that came to my mind. The only one I think could possibly rival him for that spot is LaMotta.