If there was ever an unbeatable figher it was prime Roy Jones Jr., but I still see slick defensive fighters giving him a hard time, I think he was so used to hitting opponents so easily that guys like Montell Griffin gave him a hard time when he couldn't easily hit the target, in their first fight, now put Mayweather in there and he does everything way better than Montell, and I could see how this situation could be different, but once against Roy wasn't a natural 175pounder, and 160 or 168 was more his prime weights though he became his best IMO at the 175 in terms of countering, accuracy and timing. If he would have stayed at the lower weights there is nobody I could see beating him, guys like Mayweather he would probably overwhelm because at the lower weights he didn't mind not landing punches like against Toney, he just continued firing combinations and using lateral movement with a million punching angles(talking p4p for Mayweather-Jones). Leonard at middleweight wasn't as quick or strong, but his jab and slick movement would have made this interesting. If you are talking prime Hagler vs the Jones that fought Hopkins then Hagler would probably win, but if we are talking them fighting at 168 when Jones was at lhw then I say Hagler doesn't stand a chance. He wouldn't get blown out of the water but Jones would confuse him, and stagger him with punches that would come at times he would never except, this fight would look like Mayweather-Hatton but go 12 rounds. Ezzard Charles, Archie Moore, were all good slick boxers, but they all would have lost to Jones. I think ezzard or Billy Conn had the best chance, but they still weren't quite good enough.