With rumors of a Justice League movie persisting, and new reports suggesting that Warner Brothers hopes to get filming underway in the summer, one has to wonder: will the story be completely original, a la Superman: The Movie and Tim Burton's Batman, or a loose adaptation of a story from the comics, like Batman Begins or Iron Man 3? Well, it's always more fun for comics fans when there's at least some element of an existing story in the movie. Why? Because then we can pontificate endlessly about what to expect, what will be different, and why the print version is better. If they were planning to bring Justice League to life as an adaptation of something that's come before, though, what stories might they choose? Let's see... The New 52: Origin
This ones' the most obvious choice, of course; it begins with Batman and Green Lantern and plays through to Superman before anyone else is introduced. That's pretty much in keeping with moviegoers' awareness of the characters in question, and would provide a nice first act introduction. Plus, gargantuan alien invasion led by Darkseid is a plot that almost anyone can get behind, almost anyone can understand and which has huge potential to sell toys since Darkseid and his minions are, let's face it, just so cool-looking. Also, it is by design a "first story" and therefore easily adapted with only very minimal changes, if any at all.
JLA: New World Order The first arc of Grant Morrison and Howard Porter's celebrated run on JLA, which revitalized a franchise that had been flagging for about five years, seems a pretty obvious choice, too, especially because unlike previous attempts to salvage the damaged property, it didn't involve introducing a "new and different" Justice League. Rather, it went "classic" and that seems to have been the model ever since. Also, this version of the story would not only allow them to introduce Martian Manhunter but actually spotlight the character. The New 52 version doesn't include the iconic "heart of the Justice League."
JLA: Year One This one would be almost impossible to do in any way that's really true to the comics, but only because it involves every character in the history of DC. A more focused version of the story could totally work--and it would give them the opportunity to do a pretty Batman-centric story (something that has to be pretty attractive to Warner Brothers) without actually doing the Tower of Babel story again, which they've already released as a direct-to-video feature called Justice League: Doom. It also shifts the burden for saving the day off of the shoulders of Superman, Batman and Wonder Woman and onto some of the characters that the casual movie viewer might not be as attached to, thus giving them a reason to be there.
Identity Crisis This one wouldn't work in the same way the comics did, but a modified version of the story could really play well with the movie audience. Rather than spending a lot of time establishing characters, you could open with the basic premise that we live in a world where these people with powers exist. They've got their own community--and now someone is killing members of that community, prompting a bunch of them to come together to put the kibosh on it. The benefit to this story, of course, is that it's a fantastic best-seller and has some bookstore and pop cultural cache outside of comics. It also features Deathstroke, who will be a household name by the time the film is shooting because of Arrow. The downside, of course, is that without taking the time to really develop any of the key players and "victims" involved, they'll feel pretty shallow and one-dimensional. Generic is not your friend when it comes to superhero movies; if you feel too much like somebody out of Kick-Ass or Super, the whole thing will feel kitschy.
The Final Night This one's a bit off-the-wall, but it's an interesting premise, it's got global chaos, and best of all, you don't need to spend any time developing a villain! Since Warners didn't make any movies ahead of time for the Justice Leaguers, it's probably more important we spend some time on them than anything else. Also, this could introduce people to the DC Universe at large by having the League working with Cadmus, S.T.A.R. Labs, LexCorp and whomever else it occurs to them to throw in along the way. Plus, it's a move nobody would see coming, since it's not as though it was a wildly popular comic book series. And it would "Nerf" Superman sufficiently to make the threat credible.