Justice League, Part One, or whatever they end up calling it, opens November 17, 2017.
It could be a loose reference to the video game series Injustice: Gods Among Us, which is set in an alternate Justice League universe.
I could get behind the first one, which is simple and effectively describes the movie in the most straightforward sense: a superhero crossover where the members of the Justice League unite.
From a non-comics and pure movie-goer perspective, the last three sound pretty cheesy as movie titles, especially Angels and Demons.