Which legitimately big modern heavyweight had the best endurance? By big, i mean at least 6'4 amd 240 lbs or more. I can't help but think that massive guys like Bowe, Lewis, Klit brothers, Joshua and Fury would struggle more in 15 rounders. Their massive weight would make it more difficult for them to fight at a high pace in a 15 round fight. They would still be world class but would be a bit more disadvantaged. Personally, i would love to see 15 rounders brought back especially for heavyweights. I imagine some of the guys between 210-230 lbs would benefit from them.
Vitali and Wlad. It's not just the number of punches they throw but the amount of movement they used. And also the fact they could fight until they were 40 at a very high level.
More suspect pacing and lack of relaxation. But I'd bet his long distance roadwork or swimming pace is faster than other SHWs. In some of his earlier fights he was throwing 80-90 punches a round while really sitting down on them.
Bowe for me, by a margin. Because he worked so much mid- and close range and those ranges are much more draining than being at long range. Wlad and Vitaly had good stamina, but a key ingredient was their ability to keep shorter opponents at range. It's so very much less draining if you don't particularly have to worry about the opponent's punches because the opponent is out of range. This is very clearly evident by how quickly Wlad ran out of gas when he couldn't maintain this control.
Interpreting the question slightly differently, I'll say... Jarrell "Big Baby" Miller! -6ft 4in and 280lb -Never runs out of gas (or "juice") -Never stops talking (for a second) -Blamed his latest PED failure on a sexual stamina pill An all-round superb stamina-tastic athlete and role model!