For me it is Roy Jones during the 160-175 era. He was so much better than everyone else around. It was too easy for him. Never in the hundreds of fights I have gone to have I heard the speed and power of the punches like Roy's. He fell off when gaining and dropping weight to collect belts, but in his prime......
Floyd is right up there in terms of talent as well. He's a flashier version of Whittaker.
My 2 all time favorites are Marvelous Marvin Hagler and Aaron Pryor but they were in their prime when I was like 6 or 7. Watching Pryor highlights and he is the guy who would beat Floyd at 130-144. Berto reminds me of a very poor version of Pryor.
Floyd is a genius in the ring. His skills aren't just natural. He is a hard worker. Roy was just a physical freak who got by on sheer physical assets that nobody else has had since. Wish he had been able to fight McClellan at 168. That would have been crazy.
i think a prime mike tyson was one of the greatest fighters i've ever seen. when he was in prime (id say before he went to prison) he was just unbelievable. the speed, the head movement, the power in both hands, the boxing IQ... unbelievable. remember in the junior olympics? in the gold medal round the opposing corner threw in the towel in the first round.
Mayweather is really talented. also a very intelligent fighter. but maybe we see him do so well because opponents are not smart enough to punch the body. you cant go headhunting against mayweather.. his defense is too god you'll be disappointed all fight. punch the body, then when he's forced to lower the hands you can go upstairs.