Definitely Marciano. He wouldn't have been KO'd like Frazier was. and he was down much less in his whole career. much more consistent
People tend to forget that Frazier was never really parked like a Cadillac by anyone.... Frazier was stopped after either being dropped several times or punched to death by Foreman and Ali.... Never truly parked for the 10 count... Frazier's chin was intact and reliable.... WORD! MR.BILLbbb Note: Ali still had good power in his cross prior to 1976.....
Frazier was knocked down by heavyweights who were in their primes. Marciano was knocked down by a middleweight who was washed up and another over the hill fighter so you tell me who had a better chin.
I'll pick the guy who wasn't knocked down half a dozen times in two rounds against the only puncher he ever fought.