LOL
Marciano was a vert small heavyweight a prime Ali would have killed him off of his jab alone, Marciano wouldn't get near him for the entire fight.
That said arguing that a boxer is better based on the idea that someone from one era would beat someone from another is silly. On that basis the Klitschko's would be top 5 of all time, when they aren't.
Yes he was small and light for a heavyweight but 49-0 fight record and 43 knockouts. Fraser was a poor man's Rocky and he beat Ali in their first fight and was definately his toughest apponent