Originally, I would've said John Stewart and Wally for the first JL movie because they seem to have more chemistry within the JL as a whole, however ...
Barry seems to be the in-Flash right now given that he's the sole Flash in the New 52 and that he is getting his own show (which I am really really excited about).
Due to JL War, I think that Hal Jordan could have just as much team chemistry as John Stewart (Note: I was actually disappointed by both the original GN and the JL War adaptation).
If I was to name off my first JL roster though, it would be:
Superman
Batman
Wonder Woman
Flash (Barry - because I feel he's the more 'iconic' one)
Green Lantern (John Stewart - to distance from the GL movie AND diversity ...)
Aquaman (seems like DC/WB wants to start a franchise with this one)
Zatanna (just a random wild card I threw in for more gender diversity and MAGIC)
I always thought that Cyborg was kind of awkward as the token minority of the Justice League, because that would mean that the Justice League only has half a black person. However, I kind of think he might take Zatanna's place in my imaginary roster. He's kind of iconic/popular as a member of the Teen Titans (which I think is popular with kids right now), plus its the token minority thing.
(Note: as a PoC, I prefer seeing diversity in comics)