I personally rank Marciano inside the top 5...but I won't say he could beat anybody, cus Marciano's style was beatable, but his odd-style and deceptive defense and power made him an extremly tough opponent.
Louis had a few weaknesses but he never faced an opponent great enough whose strengths were Louis' weaknesses---Louis couldn't fight backing up, he had a questionable chin, but his defense and offense made up the difference.
All I am pointing out is if Tony Galento, who was a man who brought the fight to his opponents, with as little skill as he had, with his power that wasn't as great as Marciano's could hurt Joe Louis and drop him---and that Arturo Godoy fought from a crouch, though not as good as Marciano could, and gave Louis problems---and mind you, this was Louis in his prime years, it is absurd and very biased to say that Marciano, no matter how you rank him, would have no chance against Louis.
Even Louis said that he did not think even at his best he could have beaten Marciano, and though this can be argued, I'll take Louis' word for it, cus who would know better than Joe Louis?
I rank Joe Louis at #1, only for the fact he did more with the title than any other man, in any division---though myself his opposition was weak by and large, with exception to the former and future champions that he had fought.
Jack Dempsey I rank at #2, because even though there have been others with a similar style who have won titles, nobody was better as a swarmer than Dempsey; but even Dempsey himself said he believed Marciano was the hardest hitting HW champion.
#3 I have Muhammad Ali- was the fastest yes, but lacked HW power; proved he could take a punch when he came back in the 70's, the best era in Heavyweight history. Ali often said he could not imagine what Marciano in his prime must have been like.
#4 Rocky Marciano; 49-0 43 knockouts, beat the best available, over came a late start, short reach, crude skills, to defeat the best stylists of his era. What more could you ask from a fighter, and still 50yrs later nobody has still beaten his 49-0 record.
#5 Jack Johnson.
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So, the top three men I listed over Marciano all said in one way or another that Marciano was a very tough and great fighter; Dempsey said he punched the hardest, Louis said he never thought he could ever beat him, Ali said he couldn't imagine facing a prime Marciano.
I can't say that Marciano would have beaten any of these men, but it's a disgrace that people just wipe Marciano under the carpet like he was just some bum off the street. He would have given ANY champion a tough time, and would have beaten a majority of those men---myself the only man I can't forsee Marciano ever beating is George Foreman.
Alot of people point out that Ali would have beaten Marciano due to the Foreman fight, but I don't care what anyone says, Ali didn't beat Foreman, George Foreman beat George Foreman---Ali just managed to be tough enough until Foreman was completely tired and had nothing left.
Foreman fought angry...and I don't think Ali's tactics would have really bothered Marciano, Marciano never lost his cool, was always focused and never tired---Foreman's weaknesses were Marciano's strengths.
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SO far it's 1-1 on the Marciano vs Ali SUPERFIGHT 2
Note- In the original computer fight between the two men, up until the KO the bout was 114-114 dead even as judged by the computer---Marciano badly cut over his eyes and nose, Ali slowing down from the body shots and visibly weary from the earlier knockdown's he suffered---Marciano himself was knocked down once.