I say Zora as they actually have a pretty solid military. The hylains army is scared of almost everything (exept for link), The guredo would be the closet match to the zora, both with big armys and bases hard for others to reach, however there are simply more zora than gerudo so i believe this to be the ultimate decison. The gorons, yes can survive underwater, big deal. That dosent mean they can move any faster than a human as a matter of fact they sink straight to the ground. They would easily than be dispatched with spears or arm blades. The twili is simple, break the mirror shield. As for land battles the zora would not be profficent especially against the goron however they could inhabit the waters of hyrule for most of the battle and play passive aggresive and I believe the zoras have enough witts to figure that out. They could take over castle town by using the moat, they can take lake hylia as a second base, there original base, and gerudo valleys river are all places they would have an advantage, most of them being fairly close to enemy bases. That is my analysis.