Chuvalo for sure. The guy could still probably take a hell of a shot to the face. No homo.
Made me lol irl ^ 
Just a thought. When it comes to deciding which heavyweights have or had the best chins, you have to look at the power punchers they fought and the power shots that they took (two different things, of course). For example, over the course of his career, Ali fought some huge punchers: Liston, Foreman, Lyle, and Shavers. I'm not sure that I would add Norton, Quarry, and Frazier to that list. Ali was dropped (three times and stopped by Holmes) more than Tua was dropped but he clearly fought harder punchers. I'm not saying that Tua can't take a punch, obviously, but who are the biggest punchers that he fought? Shouldn't that be factoted in?
Jase, I'm still waiting for you to respond to my Holyfield-Lewis comment :)
ron den otter - I'm not saying that Tua can't take a punch, obviously, but who are the biggest punchers that he fought? Shouldn't that be factoted in?
It definitely should be factored in.
I would say that Lennox Lewis and Ike Ibeabuchi compare pretty well with most heavyweights in history, in terms of punching power. But Muhammad Ali's resume is obviously far better.
Something else to think about though is that Ali had a movement-based style that led to him not getting hit flush very often (at least when he was younger.)
Tua on the other hand was pretty much a face first slugger who took everything on the chin.
For one cro cop isn't a boxer 2 he just got cleanly ko'd by frank fuckin Mir. And was ko'd by gonzaga somewhat recently.
Ken Norton
Tony Tucker
James Toney, Never been KO'd in Boxing, lets see what happens in the UFC...
anemone - rocky marciano was able to take some pretty decent shots
"The Rock" retired underfeated...49-0 43ko's
Good points, P4P.
I would say no to Norton, yes to Tucker (I had forgotten about him) and yes, I get the reference to Rocky I.
ESPN used to show some of Marciano's old fights. My favorite one is his first meeting w/ Jersey Joe Walcott, especially the ending.
SK, I would say that Toney's ability to avoid taking a clean shot is the key to his never having been KO'd, which isn't to say that he has a bad chin. It's just hard to tell...
TTT
Foreman and Cobb
During his first career, Foreman was dropped by Ali, Lyle (x2), and Jimmy Young. No one dropped him during his second career.
Jack Dempsey and Marion Wilson
TTT
Chuvalo or Cobb. No doubt.