Dempsey would smash Braddock to pieces. Jim was a solid performer, but not quite on Dempseys level. Braddock outworked a totally unmotivated Baer, and had a good moment against Louis (before getting pulverized), but most of Jimmy's career was up and down. Though the win over Baer was a career best win for Jim, he may not have been in his prime. The Dempsey that cut down Willard and Firpo would have pummeled Braddock, at any time in Jim's career.
Braddock was much better towards the end of his career when he became more of a two fisted fighter, therefore i take jack dempsey in 8 rounds.
I think the fighter Braddock became was better than Gibbons, who lasted the distance with Jack. He is awkward, very very tough, and has an exceptional jaw and heart to match. I think he would give Jack a difficult night. I don't say that a KO is impossible, not with Jack Dempsey in the other corner, but my pick is a Dempsey win on points.
