Mayweather is the best of them clearly, always has been.
Pac and Marquez, I don't know how to rate them anymore. Resume wise they are both great, but I had Marquez getting the best of the 4 fights and then ending it with a savage KO....toss-up I guess.
Marquez, I think retirement. Can't go out any better than that...if he does fight again, stay away from Mayweather, he's all wrong.
Manny? I dunno. He can still beat plenty of big name fighters, but how will he be after the lights going out like that? Hopefully he wins a few fights and goes out on a high.
Mayweather? Guerrero and Alvarez added to his resume is the target I believe. They would be two good wins, two good pay-days and a nice year for Mayweather.
And yes, Gamboa can.