Gondor because the dwarves (what was left of the dwarves anyways ) were beginning to keep to themselves much more, Most of the elves were sailing back to Aman. Rohan will never reach the greatness that Gondor had under Elessar's rule and the Gondorian has stronger weapons and armor.
Plus, Gondor has been holding off Mordor in Ogsiliath ( I prob misspelled it) for a long time, proving it has the best military according to other games.
It depends what elves against which at what time in which battlefield. Most commonly elves but if rohan had and uphill advantage and were against silvans then Rohan would win. Gondor maybe just maybe could win if in siege and had Fountain Guard but eny way else they would lose.