With all due respect, as a fellow Thor fan, I have to disagree. Whosoever holds this hammer, if he be worthy, will possess the power of Thor. Yes, it was meant first and foremost for Thor himself, but others have wielded the hammer. It is an elite class to be sure including Beta Ray Bill and Captain America to name two (I'd be willing to bet in DC that Captain Marvel and Wonder Woman would meet the standard). While Mjolnir's magic properties would make it a formidable weapon against Superman, it does not negate his worthiness. Like it or not Superman is the icon, the standard by which all other heroes are judged; he is not an "ass". That may be the very reason why some dislike him, that's fine. That is why he's not the only superhero we've got.
Finally Thor would trash the JLA on his own while Superman would take the Avengers apart leaving the two for a final battle, who's outcome would be in doubt. (I happen to be a big fan of both.)