Just out of curiosity, which super hero did they pick? I would imagine that Superman wouldn’t have to be too bright but I don’t know much about his character.
Depending on who happens to be writing him, Superman ranges from "smart guy but not THAT smart" to super-genius level. He's the last of a race of genetically optimized people and his parents were scientists so, I'd go with "he's much, much smarter than Batman, but Batman's power is to always have planned for everything whether or not the writers thought of it at the time."