Byrne BTC (Before The Crazy) made the argument that Cap would win because, by definition, he's the best at hand-to-hand combat, and Batman is the second-best at everything. (Possibly the World's Greatest Detective, though; point being that Bruce specializes in way more things than Steve does, without having the Super-Soldier Serum advantage physically.) I think that volksjager has already posted the Cap-Iron Fist fight here that sort of demonstrates that.