You have to break it down to level of comp and stages of their career....

Marciano beat Louis, Charles, Moore and Walcott but Louis was way past his best so I do not count that fight...Moore was pretty much the same size as Marciano give or take an inch...but a great win indeed same for his wins over Walcott and Charles,,,,

I put guys like Lennox Lewis above him because of not size but fac5t he had SO many more good HWTS on his resume and was in the second greatest era of HWts plus dominated the division for pretty much all od 2000 on until he retired......

Ali is one that needs nothing to explain same as Joe Louis in his prime ( the fact Louis held the title for so long is amazing enough).....

Larry Holmes IMO was just more sound and was dominate in his career......

I also think a prime Tyson pre Douglas would have beaten Marciano....Close in height but Tyson so much faster and bigger....not to mention had a better style....Though over all I give Marciano the credit of a higher Ranking