Edwin Valero had an endless gas tank and was in your face for however long it went. Dude was a real beast and a sad story.
I thinh this is a question that doesn't have a real definitive answer. As for some reason a lot of 90's and early 2000's boxers seemed to have an incredible gastank. They probably did a lot of cardio and ate a lot of peanutbutter sandwiches. Hard work... _edication!
I think by weight class is more fair, but these are the first names that pop into my head... Ali Fraizer Manny Diaz Calzaghe SRL Usyk Froch GGG Jirov Mayweather
Certain names spring to mind such as Super Joe Calzaghe, Ali, Erroll Spence Jr, Lil g, Mayweather etc.