This is only Roy Jones of the 90's career and Mayweather's 00's career. This doesn't include Jones's career of the 2000's and doesn't include Maywather's career of the 90's.
I've voted for RJJ but I think they're about even. I think RJJ knocked off some great fighters in the 90s and Mayweather probably has underwhelmed, but ultimately both were practically undefeated in their period, had some huge mega fights and overcame size odds to beat opponents. RJJ is the better attacking fighter, probably one of the best ever offensive H2H. Floyd is probably one of the best ever defensive H2H.
Hard to say. As pugpower said: RJJ - Greatest offensive fighter ever BF - Greatest defensive fighter ever.