I see them both in best chins in the heavyweight division with Ali being above Rocky. Marciano only down twice, against men who had 164 ko s between em. Ali was down against Cooper, Banks, Frazier and, if you count it, Wepner. Not a great deal between em, neither man was ever kod, the Holmes fight was a corner pull out as we know. Can we separate em much really?
Ali was also decked by small heavies. So maybe Marciano would walk through Shavers, Lyle, Liston and Foreman too !
The answer is who knows? Edge to Ali because his defense wasn’t as good as Marcianos (took far more punishment over the course of his career) and he faced bigger punchers. A lot more.
Ali's chin was clearly no worse than Marciano's, but it is hard to be sure whether it was better, and if so by how much.
That's the thing, Ali decked by Banks and Cooper. You can understand Smoke dropping him but Henry Cooper especially really shook him.
A breakdown of the data. Yes Ali took shots from bigger punchers, but the marks against their respective chins are about even. I don't find it far fetched to think that Walcott or Moore could have dropped Ali, or indeed that Cooper could have dropped Marciano. We can never know what would have happened if Marciano had taken shots from Foreman or Shavers. So where does that leave us? It is probably reasonable to assume that Ali's chin was not significantly worse than Marciano's. That leaves a range of possibilities, from their chins being about equal, to Ali's being significantly better. Obviously we must consider Ali's to be the far more proven quantity.
For me, he was absolutely blindsided by Cooper and didn't see the punch coming at all. As he gained more experience, that happened a lot less. He braced for impact a lot against Joe, whom he had much more respect for. (Not to demean Cooper in any way.)