I lean towards Ali, but Johnson would be a handful for any Heavyweight in the history of the division.. But I will say Ali would win a decision..
Jack Johnson would out smart and defeat just about every fighter in history. But Ali was THE greatest of ALL times! And I got him defeating Johnson in a very close decision.
I do think it would be very close because Johnson would probably use some of his own speed to give trouble to Ali.
Yet he had his hands full with spindly no-punch O'Brien, with crude Hart, with tiny Ketchell, with tiny Choynski, with no-hoper Johnson and disineterested cowboy Willard. OK. Sure.