It's really interesting to see the list. All of those fighters operated in weak divisions...all except for Floyd
Remove Marciano immediately. The guy never fought anyone that mattered and would get spanked by guys like David Tua, let alone the good professional heavies of other eras. It's a toss up between Calzaghe and Mayweather Jr - and it's not that much of a toss up. While Calzaghe definitely did enough to earn a HOF career and ATG status, he's not in the class of Mayweather Jr. You add two more wins (Mosley and Pac) onto Mayweather Jr's career and you're talking about a Top 10 ATG. You add two more wins (Dawson and Winner of Super 6) onto Calzaghe and at best, you're talking Top 50. It's that simple.
Bernard Hopkins at his age was better than the Joe Louis who fought Marciano. ****, you could argue that ODLH was better than the Joe Louis that fought Marciano. It's like attempting to state Holmes is great owing to beating cassius.