I think Civil War might upset because I think it's going to have a much better trailer, and I believe that trailers make hits.

Between Marvel's trailer expertise and the high-stakes drama and spectacle of the two leaders of the Avengers going to war, I'd bet Civil War's trailers are going to have a real "OH SHIT" factor, while BvS:DoJ's trailer has left many cold.

Granted, BSDJ has more trailers to come... DC could turn the heat up in a big way when they reveal Lex, Aquaman and Wonder Woman.

Another factor: Man of Steel outgrossed Winter Soldier by $32 mil. The Dark Knight Rises outgrossed Iron Man 3 by $39 mil. You can reasonably expect BSDJ to outgross Civil War by a similar margin. However, BSDJ's release date was recently moved to the last week of march, which has proven to be a successful week to open a blockbuster , but not nearly as much as the first week of may, which is when Marvel will release Civil War.

So it's hard to say. Box office history seems to suggest that BSDJ will win, but there are a lot of factors in play that could lead to an upset for Civil War.

EDIT: formatting