Oscar De La Hoya was past his prime when he fought (and lost to) Floyd Mayweather -- but prime Oscar woulda beat Floyd's ass ... so says Shane Mosley.
The boxing superstar fought both guys -- and beat Oscar twice -- and tells TMZ Sports he's convinced De La Hoya was the better fighter overall.
Here's a transcript of what Shane told Mike Babcock when he came to the TMZ office.
Babcock: If you take Oscar, Manny and Floyd, all at their best …
Mosely: Oscar. I think Oscar would’ve been the top one.
Babcock: Really?
Mosely: Yeah.
Babcock: Floyd likes to call himself "The Best Ever" …
Mosely: Nah.
We also asked who hit the hardest -- and that answer was surprising too.
Shane also fought Canelo Alvarez -- and says he's convinced Canelo would beat Floyd Mayweather if they fought right now.