what was the prime weight class for these modern greats

Toney's prime was 168
Roy Jones' was the same but carried into 175
Erik Morales' prime was 126
Barrera's prime was 122-126
Oscar De La Hoya's prime was 135 but carried into 147
Shane Mosley's prime was the same as De La Hoya's.

 

James Toney - 168
Roy Jones - 175
Erik Morales - 122
MAB - 122
DLH - 135 - 147
Shane Mosley - 135

 

James Toney- The best I've ever seen him perform was at MW vs. McCallum, though he wasn't really consistent enough at any weight. I don't really think he had a prime weight class, just prime fights.

Roy Jones Jr.- His prime was at 168 unquestionably in my opinion. He evened pretty much everything out there.

Erik Morales- I'd say his prime was at 122, he was just quicker and probably a little better offensively, though he was never good defensively.

Marco Antonio Barrera- In his earlier days he was more a brawler, though he was probably better physically and more active. As he grew a bit older he started to refine his technical skills and even out his pace, but he still had most of the fire left in him. I go with the consensus that his best performance was the Hamed one. Made him look a fool, as pretty much any elite fighter would though. Though his first fight with Morales, which he deserved to win, is a good choice.

Oscar De La Hoya- I'd say from 140-147 he was in his prime, but I think at 140 he'd present more stylistic matchups head to head. I think that was his most effective weight.

Shane Mosley- I think he was better as soon as he moved up to WW actually. Noticably faster than his latter days at LW, as he had begun to slow due to the weight-draining, and stronger and sturdier, in his own words. Only problem was the far better competition he faced in comparison to the wasteland he dominated at LW.