I know this post is years old but I can't help but put in my two cents here. I can see Joe Louis pulling a knockout win. Louis was flat footed, yes but he was also extremely conditioned, his trainers putting him through a regime where he'd be able to go twenty rounds. An out of his prime Louis had trouble with the crafty and elusive Jersey Joe Walcott and was put to the canvas by well timed counters. Though he eventually caught Walcott in the second fight. Louis was not only a power puncher but a precision puncher as well never wasting shots like Foreman or Liston and always learned from his mistakes especially after his fights with Schmeling and Godoy.
Ali could move, best footwork of any heavyweight. And yes in his prime he could do it for the full fifteen. As long as he doesn't get cocky he'd be fine. Henry Cooper floored and seriously hurt him in their first fight and almost KO'ed him But early in his career he was floored by the limited Sonny Banks who despite having a single punch in his resume put Ali to the canvas. Doug Jones also exploited his weakness and rocked him not half way through the first round. Truth be told if you want to rate the greatest heavyweight of all time I can't blame anyone who would have either or in the top spot. But I do think Louis was the more technical and efficient of the two.