VOTED The Flash but a close second SHAZAM
Green Arrow already has his own (amazing) television show and its realistic enough to fit in the Nolan-verse so if there is a Justice League film then I fully expect Stephen Amell to play the emerald archer in the film.
Nightwing should not and will not get his own movie unless they re-write his characters backstory which would be a crap move that fans will not react kindly to (Look at the Iron Man 3 version of The Mandarin)
Wonder Woman will most likely be the next movie and I expect Aquaman to just appear in the JL film (like Hawkeye or Black Widow in Avengers)
Aquaman's sidekick has way cooler powers than Aquaman. All Aquaman can do is talk to sea creatures, swim super fast, and has a trident. He is useless out of water.
I think it would be cool if they did a movie on the Question or Martian Manhunter.
And oh god, an Aquaman movie would be terrible. Because everyone knows Aquaman is pretty much the worst super hero DC has besides plastic man.
You obviously don't read the Aquaman comics because if you did then you would never use the words "Worst" and "useless" to describe Arthur!
He is one of the most powerful beings on Earth and he has an army that rivals the Themyscirans! He has also been one of the most complicated characters with personal issues that I wouldn't wish on Batman.