What heavyweight has the best stamina?

Jeffries, probably. He & Marciano under compromised rules would be fascinating.

 

Deontay Wilder

 

To be fair to him, was still strong to knock down Fury in the 10th an 12th round of their 2nd fight

 

I suppose you mean their first fight. Because that was the only one that went the distance.

 

Yeah

 

Frazier
Marciano
Ali
Jeffries

honourable mention: Usyk

 

I'm guessing Jefferies since he got nailed a lot and kept on trucking in bloody fights lasting 20+ rounds.

In the more modern era, Frazier has an insane late round work rate.

 

Probably Marciano, although Frazier might be able to give him a run for his money. Both were exceptional in this regard.

 

Holy had good stamina .was a machine when he was young

 

Probably Jeffries or Frazier? I'm not sure how high Jeff's workrate was during those 25 rounders though, the short snippet of Sharkey-Jeffries suggests a hotly paced contest.

 

Marciano for me. Frazier, Holyfield and Usyk not far behind.

 

Frazier and Marciano are no doubt the favorites but a prime/sober Leon Spinks had crazy stamina.

 

Carnera had excellent stamina as well.

 

John L. Sullivan? Under LPR rules, he went 75 rounds with Jake Kilrain. Kilrain did not come out for round 76. 2 hours, 16 minutes total, so the equivalent of 34 modern rounds?

For MOQ rules, Jess Willard? He knocked out Jack Johnson in Round 26 of a scheduled 45 round fight.