For those interested in Boxing history and perhaps some debate I put up my top 5's from the original 8 weight classes. Keep in mind it's not necessarily who'd beat who head-to-head more the level of accomplishments, opponents and how they measure in their era relative to all-time both skills-wise and competition-wise. I'd be interested to see others lists.
Heavyweight
1. Muhammad Ali (USA)
2. Joe Louis (USA)
3. Jack Johhnson (USA)
4. Rocky Marciano (USA)
5. Larry Holmes (USA)
Light-Heavyweight
1. Ezzard Charles (USA)
2. Archie Moore (USA)
3. Michael Spinks (USA)
4. Tommy Loughran (USA)
5. Gene Tunney (USA)
Middleweight
1. Harry Greb (USA)
2. Carlos Monzon (Argentina)
3. Sugar Ray Robinson (USA)
4. Marvelous Marvin Hagler (USA)
5. Stanley Ketchel (USA)
Welterweight
1. Sugar Ray Robinson (USA)
2. Kid Gavilan (Cuba)
3. Sugar Ray Leonard (USA)
4. Jose Napoles (Cuba)
5. Emile Griffith (Virgin Islands)
Lightweight
1. Benny Leonard (USA)
2. Joe Gans (USA)
3. Carlos Ortiz (Puerto Rico)
4. Roberto Duran (Panama)
5. Pernell Whitaker (USA)
Featherweight
1. Willie Pep (USA)
2. Sandy Saddler (USA)
3. Salvador Sanchez (Mexico)
4. Abe Attell (USA)
5. Vicente Saldivar (Mexico)
Bantamweight
1. Eder Jofre (Brazil)
2. Ruben Olivares (Mexico)
3. Carlos Zarate (Mexico)
4. Manuel Ortiz (USA)
5. Panama Al Brown (Panama)
Flyweight
1. Jimmy Wilde (Wales)
2. Miguel Canto (Mexico)
3. Pascual Perez (Argentina)
4. Pancho Villa (Phillipines)
5. Benny Lynch (Scotland)
Pound for Pound top 10
1. Sugar Ray Robinson (USA)
2. Henry Armstrong (USA)
3. Harry Greb (USA)
4. Sam Langford (Canada)
5. Willie Pep (USA)
6. Roberto Duran (Panama)
7. Eder Jofre (Brazil)
8. Ezzard Charles (USA)
9. Benny Leonard (USA)
10. Carlos Ortiz (Puerto Rico)
Obviously very open for debate and occasionally the lists change a little bit since so many great fighters are hard to separate. Some modern-era fighters like Roy Jones, Floyd Mayweather, Manny Pacquaio, Juan Manuel Marquez etc; are clearly great and even better than some of the fighters on the lists but due to this being a 17 division, 4 belt era often move around more and don't get the same kind of lengthy stranglehold on divisions as in the past.