Mayweather hands down.

As many awards in all sports, Fighter of the Year is also a popularity contest as much as a recognition of achievements. By the end of the year Mayweather will have been involved in the two highest grossing fights of the year, not to mention the highest grossing fight in history.

Besides beating the best 154 lber (which Oscar was at the time even though we don't want to admit it) and the best 140 lber in the same year is a pretty big achievement.

Of course this changes if he loses.......but he won't lose.