People put to much weight on "chins", there have been a number of fights recently that have dispelled this garbage (Kirkland v AA, Areolla v Strivene, Rigo v Donaire). However, to answer this "chin" question with another exaggerated theory: Hearns! The fact is that his punch resistance was not that bad but he is perhaps the Greatest fighter ever with a questionable set of whiskers
Wlad has been stopped twice due to punching himself out. Lennox has been KOd twice by one punch. Wlad has the better chin.
Lewis was the first guy that came to mind. The only top level HW champ taken out early twice by grade B fighters when he held the title. The only one. To deny that his chin wasn't shaky is to deny reality! :nod
Terry had such heart but his chin was not good at all. I remember Simon Brown hurting him with a jab.