Frazier and Marciano are at the top, Holmes' workrate and outboxing ability isn't enough. Marciano I give a 50/50 chance of knocking him out as well, so maybe Frazier? Liston was holding his own points-wise against young Ali (I had the rounds 3-3) before the shoulder tear happened.
Liston couldn`t cut the ring off on Ali at all, Cus D`Amato told Ali the fighter with the best chance of beatingb him was Marciano.
Ali himself says Marciano would give him the toughest fight. Many of his contemporaries and Joe Louis himself said Marciano would beat Ali