lewis duh
Modern athletes are way more far in shape and conditioning then athletes in the 40's,50's era so Lennox Lewis fought Holyfield,Tyson and beat them . The interesting question is what post 2000's boxer can do in the peak of boxing in the late 60's ,70's and mid 80's when it was the best prime era .
lennox wins unless it goes past 12 rds e.g. 15 rounder.....marciano might get to lewis late rds 13-15 for a ko....the size difference holds marciano back...but if marciano gets close he stands a good chance....remember marciano ha d heart as well as power....he was really battered in a lot of his fights but still managed to win.
lewis too much of a weight advantage, he would 1-2 marciano until his face was completely swollen and the fight stopped
both in there prime
