Probably Wonder Woman. But I would laugh so freaking hard if Captain Underpants actually wins. I mean, if freaking Boss Baby can make more money than Ghost In The Shell, anything is possible.
As hilarious as it would be for Captain Underpants to win, I think any mainstream superhero movie is gonna win in this day and age. Unless you're going up against Star Wars or the movie itself is Fant4stic.
Maybe Captain Underpants.