I think between Civil War and BvS, it will be pretty close at the box office. We all know the Marvel stuff pulls in the numbers but Batman and Superman (especially Batman) can do big numbers too. Both should do great but I might give a slight edge to BvS.
But as for movie quality, I expect Civil War will be the better made movie. The Russo Bros delivered big time with Winter Solider, and Civil War is looking every bit as good, if not better.
BvS is only the second connected DC Universe movie, following Man of Steel (which was good, but not Winter Soldier good) and Zack Snyder movies can be hit or miss, so I expect BvS to be more style over substance, like a lot of his movies, but hopefully still very entertaining.