Tyson, Lewis, Marciano are all good picks. Liston at 3 always seems a little high to me. I don't agree with the Holmes picks for the simple reason that he didn't fight the best and struggled too often against quality opposition. The Weaver, Witherspoon, Snipes, Shavers, and Norton fights all occured at or very near to his prime.
Walcott and Charles were better fighters than anybody Lewis ever beat. Lewis is a bit unproven against absolute top level. Not his fault, people just didn't want to fight him. A fight with Bowe or Holyfield a few years earlier would of told us a lot.