First time i seen Floyd at 130 against Jesus Chavez I thought he was the p4p1. So i'll go with Floyd.
Mayweather is my favourite out of the two, but Roy was sensational. That knockdown when he had his hands behind his back ridiculous.
Roy against someone like Brannon was more wow than any Floyd fight. Floyd was quicker on the trigger counnterpunching, but didn't have Roy's combination of hand speed, creative use of angles, and power. Floyd's speed and class against guys like Gerena or Carlos Rios was dazzling, but watching Roy in his prime was jaw-dropping in a way that Floyd never was.
I think Roy was possibly the most athletically gifted boxer of all time while Floyd is the most mentally gifted fighter of all time. When a fighter reaches the level of true greatness its impossible to compare them to another fighter who also reached that same level i'm terms of who was better. I believe there is a pinnacle point where a fighter simply dose everything possibly right. It may not happen in every fight or at every moment in every fight but some fighters in their prime just go into that zone and they are simply untouchable. Roy and floyd are just two fighters of many who went into that zone consistently at times in their career.