Originally Posted by Homicidal Hank
Whether judged on a head-to-head or a legacy basis, Joe Louis cannot be ranked above Muhammad Ali.
Ali was never knocked out. Louis was twice knocked out, both times brutally, and once when he was prime. Ali was more durable.
Ali regained the world championship twice after losing it. Louis lost the championship and never regained it. Ali's experience allowed him to dominate the division late into his career.
Ali lost his title to full-sized heavyweights (Frazier, Spinks, and Holmes), whereas Louis lost his title to a man who weighed only 184 lbs, in actually a beefed up career light heavyweight.
Louis defended his title six more times than Ali (19 vs. 25), but Ali's title defenses were against infinitely better opposition - Liston, Patterson, Williams, Folley, Lyle, Frazier, Norton, and Shavers. Louis faced no fighter as champion reasonably regarded as a top 10 heavyweight. Indeed, I don't rank any opponent Louis faced as champion in the top 20 all-time heavyweights.
Louis won the championship against a journeyman (Braddock), whereas Ali won the championship the first and second times against all-time great heavyweights (Liston and Foreman), two fighters I (and many others) would pick to beat Louis.
Louis was floored numerous times in his career (Schmeling, Braddock, Galento, Baer, Walcott), whereas Ali was floored only three times - the first two times when he was a young fighter, and the last time by all-time great Frazier.
Film of both fighters show that Ali's jab was superior, his foot movement was superior, and his reflexes and overall speed were superior.
The tale of the tape shows that Ali was taller, bigger, and had a longer reach.
Ali was an Olympic champion.
There is no rational basis to rank Joe Louis ahead of Muhammad Ali on any substantive top-ten list, whether head to head or legacy.