It's outright war. I'll go with Marciano. Although Evander was a great fighter at Cruiser, he was still relatively inexperienced at the world class level. I still think he was good enough to make it close though. Their styles play into one an other.
As whiskey said, cruiserweight Holyfield probably isn't seasoned enough. I'll go with Marciano by decision... Evander takes a beating late. Holyfield whips him at heavyweight.
I think Holy's reaction to aggression, fight fire with fire, both makes this a marvelous fight but also plays into Marciano's hands... I too like the Rock by decision in a brutal fight At heavyweight, that same "flaw" is the reason Holy would win... he's a much bigger guy there and it would be Marciano, unable to adjust, who would be on the losing end, likely via KO
I think its a distance fight at both weights, with Marciano winning at Cruiser and Holyfield returning the favour at Heavy. They were both filthy fighters at times, so thatd be interesting to see as well.
holyfield wins and wins handily. his speed and legs would be big factors. if you want to go by the young version who fought at 190 then its a closer fight. if we consider the early heavyweight holyfield who could have still easily made 200lbs he wins by beating the living shit out of marciano.