I can't really tell who would be on which side, cause I don't know much about Dc as I do Marvel (Still Spider-man joining was a big surprise to me) but anyway. If batman was like Cap, I could see him surrending if he saw a little boy next to his dead parents due to the fighting. And he be "OMG........". If it's Supes he would be more like Cap. Watching the people of new York Attacking him and he notice the destruction. And wouldn't this like Kingdom Come?