Fuck it, I'm gonna say Tyson's greater too, though it's arguable. Mike actually has more scalps on his record that were prime, natural heavyweights than Marciano has - I.E. Ruddock, Tucker, Thomas, Bruno. Both of them are known for blowing out faded guys, and guys who were really light heavyweights, but Mike did so in more dominant fashion. I'm gonna say Mike was greater by a slim margin, and better by a clear margin.
Marciano IMO. Although his best scalps were "aging" HoFers, Rocky beat ones that were still actively competing (and winning) at the top level (in contrast to the laid-off Holmes and the semi-retired Spinks who had fought just once in the previous 2 years and never beat another ranked opponent after Holmes). On top of that, Rocky showed more resilience in his career and never allowed himself to be beaten (let alone dominated by a Buster Douglas-level fighter) while he was still in his physical prime.
Id go with Tyson. Just about. He's simply a more seminal figure, through the initial reign, the youngest ever, the comebacks everything. He's also a zeitgeist figure. Nothing says 80s money, 80s NYC and 80s sports quite like Mike. Donald Trump runs him close on 2 out of 3. I can imagine 50s boxing without Marciano. Its hard to imagine the 80s without Mike. Hagler loses in 87...after that, Mikes really the biggest thing around.
