if they fought when? depend of the year... a green liston 10-1 in 1955 after of the rematch with marshall weighed 202 pounds and was very green, he is not beating rocky at that time and he would not be even the stronger man in the ring.
I posted a thread similar to this a few months ago, I think an older Marciano would beat a green Liston. A few posted that Marciano started having back problems later in his career which led to his retirement. So it's up in the air.
prime vs prime i go with rocky too. Liston is not Foreman stylistically or physically, marciano would avoid that jab and would work the body pretty hard, rocky would get knocked down once or twice but he would last until the point that liston was tired and lost confidence in himself and then rocky would go with all the arsenal pretty hard making pressure and stopping an exhausted Liston in the round 11
Marciano wins in my opinion but its no disgrace certainly.....Liston was still a monster but a little slow
I genuinely believe Rocky is the better fighter but Liston is not far behind him. Give Liston a 20 pound weight advantage and it's a fairly easy call to make.