Looking back at the suggestion of Martian Manhunter forming the Justice League, I think Green Lantern would make more sense. Superman, Batman, Wonder Woman, and Martian Manhunter are all solo players and are usually hesitant to be part of a team effort. While the same could be said of Flash and Green Lantern, I feel that Flash would be happy to throw in with a larger group. Meanwhile, GL is responsible for an entire sector, Earth being less than a blip on the interstellar charts. Makes sense he would assemble the Earth's mightiest defenders to protect the world when he's off throwing down against the likes of Parallax or the Qwardians.