See...I think it's the whole "Bad boy" mystique girls fall into... I mean, let's face it...
He's hot, he's fit, he's mind blowlingly rich, he wears leather, he has a GREAT car and he has this great rumbly steel like voice.
Batman is MESSED UP. The guy saw his parents gunned down and then spent years training himself to fight criminals (a superstitious and cowardly lot!) and dresses up as a BAT. The guy sees himself as Batman and Bruce Wayne is his costume.
He's grumpy, he's pissy, he's rather machivellian working within his own self imposed constraints and let's face it...he is NOT good with kids. Any kid he likes...he takes them...he trains them and puts them in a brightly colored costume to run around with him (Carrie Kelly aside...what number of Robin are we on now...and boy Dick Greyson grew up to HATE him!)....and he's NOT invulnerable! He can get shot and burned and beated and cut and scarred and it'll happen repeatedly. This guy is NOT going to settle down and have Batbabies.
He is going to stand you up repeatedly, he's going to flirt with Catwoman on rooftops and more than likely endanger your life more than once either because you are a target or because he'll use you as a target to bring down his quarry.
Superman is hot, he's fit and he can fly you around the world on your first date. He is sincere when he says he is here to fight for truth, justice and the American way. You might get in trouble but he'll always catch you in time.
Well...according to Larry Niven's essay unless you too are superstrong and nearly invulnerable ...you're not going to have much of a sex life.
His day job, he's a reporter so money is going to be tight. Sure, he can do that "coal into diamond" trick but ...he's Superman. He's not going to do that just so his family can live a life of ease.
His idea of a getaway is in Antarctica full of relics from his homeworld. Don't expect Disneyworld.
Everybody loves him ... and he loves everybody. Where do you stand exactly...?
Marriage &/or Lifelong committment:
Don't care about Bat or Supes? Who'd you pick?