For me, pretty much depends what kind of power the younger Ali could take. Assume he´d mature, tier 1 HWs are: Ali Holmes Lewis Tyson Not sure about Foreman (slick mover vulnerable) and Wlad (pressure/defensive vulnerable). Honorable mentions are Vitali, Bowe and pre layoff Fury, who was just a very big very well moving thread. Coulda shoulda might me Ibeabuchi due to good stamina, durability and power, but vulnerable to movers with reach. Overrated in H2H therms for me might be Louis/Frazier (too power vulnerable) and Holyfield/Liston (outbox vulnerable). If its 15 round fights, Tyson might drop out of tier 1, but did look stamina solid for 12 on other ocasions. Sry if I forgot someone.