If we are looking at just Floyd's performance and not the circumstances some fighters were under...I'd say Marquez, Corrales, and Canelo.
I'm a big fan of the Alvarez & Chavezfights. Even though the cw takes some of the shine off it, Lineal JMW Title bout vs a young unbeaten unified champ, I thought it was a entertaining technical chest match. Scored it 8-4/9-3. The Chavez fight was a war were Mayweather consistently changed looks to wear down and eventually stop Chavez who went on to win Titles at SFW&LW afterwards
Marquez (even with the weight issue, outboxed and dominated a master boxer almost every minute of the entire fight). Canelo (master performance against a younger, bigger, stronger fighter) Corralles (extraordinary performance moving up in weight. Gets a little too much credit for this one though--in hindsight, I think that Chico was always a limited, overrated fighter)
I have a problem with the Gatti fight. Yes, it was an impressive performance by Floyd, but Gatti simply was not on the level to compete with Floyd. RJJ was not at all shocked at the annihilation as many boxing experts and 'educated' boxing fans knew the fight was a huge mismatch. The Mosley fight was an impressive victory now that I think about it. After getting nearly knocked down and going straight at Mosley for the remainder of the fight and making him look baffled is really amazing. Again, yes Marquez was new to the weight and Floyd did not make the negotiated weight but Floyd NEVER imposed his size and strength on him. He simply made Marquez look really bad by boxing beautifully. By the way, Marquez called him out and was willing to move up in weight to face him. As much as I don't like Floyd most times, you can't blame him.
Roman Gonzalez would fight Floyd at 147. The point is anybody will fight Floyd. No matter how much you have to starve or give up in size. He's a bigass cash cow.
And should have But he didn't even try Not out of respect & not to carry him but his usual safety first style of fighting. Which cheapened his efforts that night. Castillo & Ricky hatton were great career defining performances. I actually liked his performance against castillio that's was a close fight & Floyd show everyone something different that night 12 rounds of fight. His best performance to date for sure.
Without a doubt Floyd Mayweathers best performance of all was his impersonation of a fighter . Man he sure fooled a lot of people & conned them out of their $$$$$$$ He deserves an Oscar