As awesome as I think Gyarados is, I'd have to say Gyorg would win. A sea dragon is tough, but Gyorg is a murder fish. Looking at Majora's Mask at a pokemon view, Zora Link had to ram into it while covered in lightning several times. Gyarados would go down in one or two good electric strikes. Gyarados's attack pattern mainly relies on devastating, but slow attacks. Before having the chance to loose a hyper beam, Gyorg would have rammed Gyarados. Gyorg is fast and vicious, and wouldn't let up until Gyarados was dead.