Re: Floyd Mayweather V Roy Jones (not a fantasy fight)
Both supreme talents but Jones looked nigh on unbeatable (Griffin 1) aside until about his 4th weight class and his fight with Eric Harding (but then again he didn't struggle after that until Tarver 3 years later). That aside he dominated every fight he had and never lost much more than 3 rounds in any other fight including the Hopkins and Toney bouts.
Floyd has some good wins but he had problems with a well past prime De La Hoya, a debatable (although I still thought Floyd edged it) win over Castillo and shipped a lot of punishment against a Cotto that was past his best and had been dominated by Pacquiao.
Jones' legacy is hurt by not fighting Benn,Michalzweski and Eubank (all easy wins for Roy imo) but for every missed opportunity for Roy you can find a Tszyu, Margharito and Pacquiao fight missing from Floyd's resume (though I'd favour Floyd in these as well).
Roy was much more spectacular to watch and could punch and that counts for something as well so he gets my vote.