Roy Jones up to 2004
Pacquiao
Mayweather
Bernard Hopkins
Joe Calzaghe
JMM

are all top candidates, IMO Pacquiao has to win... for now. Mayweather could still beat him this year and that would place Floyd at #1.

My order would be
1. Pacquiao
2. Bernard Hopkins
3. Mayweather
4. Calzaghe/JMM
5. RJJ

That being said I think Roy at the turn of the millenia kicks the crap out of these other guys p4p.