Endurance - Who's among the best?
I remember a quote on Chuvalo about if every fight went a 100 rounds he'd win every single one of them.
Marciano and Jeffries were both iron men who seemingly never tired and were both capable of late, one shot KO's.
Cotto comes to mind with current fighters. Not an ATG great or anything but his entire career is filled with late knockouts, including more than a few 11 round ones.