You two, fight to the Death!
No explanation needed
You already know the arguments: Superman wins because he is invincible, but Batman will win because given enough time, he'll think of a way or invent a way to beat Superman. Or he'll read a Frank Miller Batman miniseries and see an obvious way to pummel and humiliate Supes.
But with Frank Miller and Batman/Superman, he always wants to throw in Wonder Woman too.
