I would have to put Floyd Mayweather, Jr. as a top 5 all time fighter if he beats Ortiz, Pacquiao, Martinez, and lets say a random one or two more..hey look at the following criteria:

Competition.. unbelievable
Jump in weight classes..amazing (watch the chop chop or gatti fight)
Olympic games (like RJJ, should have a gold)
Dominance over his opponents ( Castillo and De La Hoya were close...and thats pushing it)