Marciano. I think he expended his energy a bit more wisely. He got pretty much the same results with less movement and seemed to have more energy at the end that was ready to use. Frazier closed the gap quicker, however.
Marciano -Genuine two handed puncher unlike Joe -Huge workrate -broke down a wide range of more skilled boxers -Huge KO PCT -Knockouts from 1 punch and accumulation I think Frazier cut the ring better and faster, and slipped and bobbed more fluidly, but really Marciano is a top 10 swarmer, as much as i criticise him.
Joe Frazier was more effective, miming his style after Henry Armstrong and just about perfecting the bob and weave style. He also had some of the best footwork, workrate and stamina I have seen. For a swarmer style, you can't get much better than Joe Frazier. Rocky was great as well and is in my top 5 favorite fighters, but I think Frazier edges him out in many areas.
Marciano had problems with Charles smothering his shots in their first match, taking away Rocky's punching room. Tommy Gibbons did the same thing to Dempsey in Shelby. Nobody successfully smothered Frazier's punches inside in that way. If, given this style from an orthodox stance against other orthodox fighters, I've rather have a premium hook than a premium right. It's a more serviceable punch, a lower risk to unload, and requires less room to uncork. Joe's right uppercut was an excellent short set up shot (witness the one he raked Ziggy's head with just before the sleeper), and he dug that right well to the body. In 1969, he outswarmed and outlasted a trigger fisted peak Jerry Quarry after seven rounds of torridly paced close quarter action in Ring's FOTY. Even past prime, he looked like a category five hurricane swamping the hopelessly outmatched Terry Daniels.
Frazier, although being heavier, was far quicker with both hands and feet and just seemed mored relentless. Marciano always seemed slow and ponderous to me. Plus, I think he seemed more deadly because he was chasing mainly older, past their prime fighters. I can't see Marciano being able to apply the kind of pressure against young strong mobile fighters such as Ali, Quarry, Ellis, Mathis in the same way Joe did.