The man that gave Floyd is toughest fight.

[BOXEO _]

Castillo beat him


next i'd say Cotto, Maidana 1, and then Augustus in that order

[Ham Porter]

The toughest fights void ever had was against Castillo. That's right, even the rematch in which Mayweather fought as conservatively as possible and Castillo still took four rounds from him.

Void will never acknowledge Castillo as his toughest opponent because of the controversy of the first fight, which is silly because Castillo was very good in his prime and likely the best fighter Mayweather ever beat (in terms of where he was when Mayweather fought him.)