Wilder by a country mile, even when he knew he was on his way to getting sparked by Fury in the third fight, he never gave up trying, even hurting Fury in the 10th i think it was. Joshua would have swallowed like he did against Ruiz or ran around all night.
I'd say Wilder but he's cried about it so much about mythical conspiracies since that it devalues him for me. In terms of in ring heart, I'd say it's a weight that we struggle to find real courage in of late. They don't have to make weight so escape the pain of all other divisions, and they can earn disproportionately to their ability as everyone wants to see HWs. I'd go for Holyfield, despite massive PED use, he had real cojones to fight Tyson and then in his 40s to fight Valuev as the away fighter.
The question of which heavyweight (HW) boxer has shown the most heart in the ring is subjective and open to interpretation. Many heavyweight boxers throughout history have displayed incredible heart and determination during their fights. Fighters like Muhammad Ali, known for his resilience and ability to come back from adversity, demonstrated tremendous heart throughout his career. Mike Tyson, with his fierce intensity and relentless fighting style, also showcased a great deal of heart. Evander Holyfield's unwavering determination and ability to weather storms in the ring earned him the respect of fans and fellow boxers. Additionally, fighters like Joe Frazier, George Foreman, and Lennox Lewis, among others, have all demonstrated their own unique forms of heart, showing grit and determination during their fights. The concept of heart in boxing encompasses the ability to push through adversity, display courage, and fight with passion. Determining the boxer who has shown the most heart ultimately depends on personal perspectives and interpretations of what it means to demonstrate such qualities in the ring.
Wilder, obviously. Joshua showed heart against a very poor Klitschko but nothing since. Wilder is a freakin' warrior.
The underrated Povetkin vs Huck war both fighters deserved the upmost respect. Deserved to be a better known fight.
Herbie Hide against Riddick Bowe. A Cruiser against a massive Heavy, Hide kept getting up. I laugh as I say this but shades of Frazier against Foreman, the man kept getting up.
Don't confuse heart with pride and stupidity. After Wilder v Fury 2, Wilder publicly went on a tirade about the following for months on end: (1) Fury was cheating him. Glovegate. (2) The referee was cheating him. "Crab in a bucket" (3) His corner were cheating him. Fired Mark Breland. The result being in Fury v Wilder 3: (1) Fury wanted to give him a slow and prolonged beating. (2) The referee wasn't going to stop this. (3) The yes men in his corner would be too scared to stop this. (4) Wilder put himself in a position where all he could do was take his beating. Wilder beat the count twice in Fury 3, that shows heart, but he needed someone like Mark Breland in his corner, looking out for their fighter's best interests, and not just their own pockets. Joshua beat the count 4 times against Ruiz Jr., that obviously shows heart, but he also needed a Mark Breland in his corner, putting their fighter first.