Come on, now. It will always be Batman, because DC editorial will let Batman beat anyone a writer asks permission to beat up, even if it's several absurdly powerful characters all at once.
The modern comic reader's expectation is that Batman can beat anyone with the proper strategy, and the writers comply. And he doesn't even have proper powers! So he's a normal guy who can use gadgets and the almighty "prep time" to do virtually anything. Even if he has to travel through the entire span of human history to do it. Riiiiiiight.
And yet, when necessary his abilities contract to make a gangster like Two-Face or Penguin a competitive nemesis. But then tomorrow he can take out a guy who can vibrate through time and space. Batman is the cheapest character because his capacities are wildly different from writer to writer and even sometimes from story to story. Yes Hulk's strength level varies a great deal between stories and sometimes reaches into the stratosphere of absurd, but it's nothing next to what one normal guy in the DCU can apparently do with 50 gajillion dollars. Batman would just have some calming....emitter...thing. He would have the perfect solution just as he always does. World War Hulk would have listed an hour, tops, in the DCU.
This isn't about personal stakes though, it's about who is "cheapest." I don't see how this point is relevant to the question at all.
The fact that Batman can so confidently put all that on the line to do what the hell ever he's required to do whenever he feels like it just adds to the cheapness. He knows he'll win! He's the goddamn Batman.
