While doing an interview with ESPN Deportes to promote his boring fight against Andre Berto, he was asked to choose his top five boxers of all-time. Instantaneously, he put himself at number one, but if you expected anything else, that's your own fault.
The more interesting part is that he put Muhammald Ali at #5, behind the likes of Roberto Duran, Pernell Whitaker and Julio Cesar Chavez. On top of having Ali at #5, he omitted boxers like Joe Lewis, Rocky Marciano and Sugar Ray Leonard. Worse than that, out of the ten boxers he had to choose from, Joe Frazier wasn't even on the list, which is an injustice in its own right.
In fairness to Mayweather, he did explain each selection, which you can see in the video above, and his reasoning is actually quite sound. Debatable, but sound.