Lennox Lewis Joe Louis Muhammad Ali Jack Dempsey Rocky Marciano George Foreman Wlad Klitschko Tyson Holyfield Holmes Pretty hard pick for me personally. Right now I am undecided.
I'm also in the Lewis camp. The thing that sways it is I think he has an edge on Tyson, Wlad, and Holmes whereas I basically see Ali as a question mark against those three. Ali might have had enough to beat Lewis, but I'm not sure about those three I named.