A combination of power, accuracy, consistency, timing, stamina, ability to hurt high caliber opponents etc. Mine: 1. Liston 2. Wlad 3. Tyson 4. Louis 5. Frazier Hounourable mention (in no order): Tua, Foreman, Dempsey, Marciano, Morrison, Brewster, Cooney, Cooper, Edit: adding Floyd Patterson to honorable mentions.
Good list! Not sure about a top 5, but I think top 3 would be Frazier, Dempsey and Liston (no particular order) HM: I'd add Floyd Patterson
Without specific order (bar chronology) : Frazier Cooney Tyson Morrison Tua Honorable mentions : Weaver and Wlad
I see two very different categories her. Fighters who were over reliant on their left hooks, and fighters who made it just another part of their toolbox.