I'm going with Carnera by KO... Primo Carnera is certainly a propaganda champion made by Mussolini's Italy and his fascist regime, but he was mentally stronger than Makhmudov, who after 5 rounds had no more juice. (Even if in his last fight against Allen he took the time to beat him on points, Allen was too inactive).
Carnera did not punch his weight ,against a man his own size who can bang he would be in real trouble.