Tua Ibeabuchi W Klit Ruddock (if you call "the smash" a hook) Frazier maybe, although I dont think he had the one-punch power of Tua and Ike at least
Tua, Louis, Tyson, Morrison are the first to come to my mind. Liston, Dempsey, Big Cat Williams all had mean left hooks as well so any of those really could be in the top 5.
David Tua Sonny Liston Razor Ruddock Joe Louis George Foreman Cleveland Williams Tony Galento Joe Frazier Jack Dempsey Sam Langford Jersey Joe Walcott- Wild Card Pick Lee Q Murray - Wild Card Pick Lennox Lewis- Highly Underrated(when he actually used it) Mike Tyson Wladimir Klitschko Mike De John- Wild Card pick Rocky Marciano Michael Dokes (Not in Order)
Frazier, Louis, Tyson, Tua and Morrison would probably be my picks. (In no particular order). I don't really count the Smash because it's also part uppercut, although that being said Ruddock's normal left hook was pretty lethal too. Honorable mentions include Dempsey, Williams, and one I'm surprised hasn't gotten any mention yet; Patterson's leaping left hook.