remember, superman is an alien, he's a good looking version of martian manhunter, he can't be saddled with a lois lane, he needs a wonder woman, who if i remember correctly is a demi-god made from/out of b/c of the earth? from gaia and zeus? i think currently they've given wonder-woman the pantheon of all the greek powers (i think she can even do lightning bolts somewhere), she's about the only thing as powerful as superman, and she doesn't have a superweakness like kyrptonite. in a sense only a goddess will do for superman.
but superman v batman? there is no way to even make that a compelling story without bringing down the power level of superman 100fold. batmans greatest strengths would be technology + smarts. Superman defeated a genetically perfect engineered general of doom(zod) backed up by super alien tech, heck the latest batman movie has him in a helicopter... superman was laying waste to a planet destroyer in the sky.
one of them will have to play dirty, or evil, that's why while flawed at least frank millers version has batman doing shit, "hey one armed green arrow, why don't we pay back kent!" there isn't a story here, because it will be shitty, there is too much goliath for david to overcome.
