Too many Streetfighter fanboys in this thread. ^_^
As for Batman vs Superman, depends.
In a spontaneous, "Okay now you two kill each other," Superman wins. Easily.
In a situation where they both have time to prepare it really depends on the Superman.
The original Superman concept was a person that was better in every way: physically and mentally. As he made the transition from medium to medium, Superman has not only gotten weaker and weaker but also dumber and dumber (also his powers have slowly been vanishing). The original Superman and the original Hulk are probably the two most unkillable heroes in history. Both are no longer such in more recent print.
It also depends on the Batman, though less so. There are two main versions of Batman which I'll refer to as The Caped Crusader and The Dark Knight. The Caped Crusader is the classic Batman with a streak of honor and kindness. He's a good person who fights crime using his tools and his mind. The Dark Knight is different; he's the cruel one that fights dirty, sacrifices others to take down criminals, and is out for revenge against all criminals above all else. I'd rate the Caped Crusader as having higher odds in a fight simply due to good karma. ^_^
