Personally not a huge fan of either. Always found Superman to be just...too damned powerful. Has every power and that's pretty dull. As for Batman...anyone who knows me knows why I can't stand this boring ass "hero". With that said, Superman dominates Batman with ease. I'm amazed anyone can say differently with a straight face.
Someone once asked the great question of who would win in a rap battle, Batman or Superman. The answer is the Flash. Always Flash.