George Chuvalo explained that his short neck and his work on developing his shoulder blade muscles is why he was so good at taking a punch.
Floyd Mayweather Jr. easily should be in top 10. On a different level ... Heavyweight, Merlin Wilson. Wow what a chin
George (S****iron) Johnson, who fought in the 1970's, had great chin. Vito Antuofermo had one of the greatest chins. Middleweight Benny Briscoe had good one too.
Because the system laughably censors words, even WITHIN words, that can be considered "bad". No not Mayweather, once again we are talking about absolute chins, not lb. for lb. Mayweather also avoids most punishment. Anyway he could not possibly approach the top 1000 chins ever. Valuev? How many could even reach his chin with excellent power? I think due to his size & scary face/skull even top HWs were sometimes intimidated by him, though he did not hit especially hard.
There are two things to consider at least. Ability to take a punch and the ability to take punishment. Chuvalo has to be on top during the modern era. George attributed his ability to take a punch to his thick neck and "big head". Ali. The bombs he took from Shavers had Ali out on his feet. Same with Frazier. The guy could take it but not only take it....take it and win.