When did it start and when did it end? I remember him coming out as a pro in prime and kept it up till he retired. His style change quite a bit as he moved up in weight class from a blur and powerful to elusive and economical. I think his prime was around end of his 130 reign to 140. Although he may have change to a slower pace he became more accurate. Also most people considers a fighter in prime when they are on the top getting big fights.
His prime was the Corralles fight with his HOF performance. Moved up to WW for the money. He was effective but would have had his hands full with Margarito or Williams.
Chavez not even merit a mention? Personally I believe it's Arguello, but I think it's a three-horse race not just a two.
Chavez gets a shout, but the most interesting mythical match up is Floyd/Arguello. Over 12: Floyd UD. Over 15: Arguello TKO or KO. If PBF fought back in the day, he would have been fine in 15 rounders, but against El Flaco Explosivo you're giving the man who normally owned those champioship rounds and extra 3 to get the job done.