I don't know about the best chin ever. He was good at avoiding damage.
If you rewatch the Lewis fight, he may have been slightly ahead on points, but it was closer than you think. Vitali was getting fucked up. Lewis would have found that chin pretty soon, as a couple more shots to that eye would have left him blind and leaking. And it WAS Lewis's last fight.
I think he's probably the HW goat. Definitely the best of his era, and his era was definitely the strongest in HW history. The 70s was strong too. Ali was the best. But the 2nd best of the 70s (Frazier or Foreman) wasn't as good as the second best of the 90s (I'm thinking Bowe, Holyfield, or Tyson). It's all hypothetical....
Anyway, it's good to discuss it with someone that is thinking about it rationally.