This is actually an interesting fight. Both feed of fear. Now, at the high of his power Superman was feeded by the whole world and he was not afraid, which is an advantage, should we take this Superman, the same or almost the same can be said of the Sepent, young and powerful, fed by the fear of the World he should be on the same level. However, Supermans display of power was far better imo. The only thing is, could the Serpent somehow break the rings connection to the fear and take it for himself? If not I think Superman would win.
Sinestro with Parallax should be interesting too.