It can be either one. Each have a strong argument to rated #1 Heavyweight. Some days I have Louis at the top, on others I have Ali.
Ali is the greatest of of all time of prize fighters, this guy has fought most of the top 20 HW of all time, had to give up 2 years of prime boxing, had awesome comebacks, exciting to watch inside and outside the ring, never ducked anyone, theres tons more to say. Louis is a close second imo.
Ali had ATG Heart - he just went after the craziest fights. A true Boxing icon and to mention Floyd Mayweather as being in the same league as him is nuts.
I can't see how anyone can dispute Ali being the best heavyweight of all time. He has 3 top ATG heavweights on his resume in Liston, Frazier and Foreman. No heavyweight can compete with that.