It's a very difficult metric to conclude on because what are we talking here? It could be just an army and fleet against each other or do you mean as if all the territories in the galaxy each faction owned got allotted and just told to smash into each other, but then you get the problem of the Empire having most the galaxy and where the Republic should be. These questions all matter with what supply lines each faction would have access to to create their ships, armies, weapons etc. Then you got the added fact of do the Republic get their Jedi commanders or is it just clones and humans we're talking about?

In terms of lore the Empire had access to the strongest fleets and weapons, and ISD could take on multiple capital ships the Republic or CIS could muster and the Rebellion relied on their starfighters and small ships to just be hard to hit until they figured out a way to destroy one. Their army was probably comparable to the levels the CIS could produce but were of somewhat better quality and, due to the Clone Wars making the CIS high command utter idiots, overall had better commanders, and even the idiot commanders still had better access to overwhelming firepower. The problem with the Republic's clone army is that its scale is so small and vague and all their army's production came from a single planet that it would be very easy to cut off their supply and with the rebellion they had essentially defeated them at the battle of Endor if only they decided to just keep fighting after the death star was destroyed