A DC, the only specific characters you can depend on to be omnipresent with high profiles are Clark, Bruce, and Diana...after them, maaaaaaybe Aquaman, too. Green Lantern and Flash will usually have big roles in the universe and publishing line, but you can never really be sure who Green Lantern and Flash will be. It varies (sometimes a lot) depending on the time and what incarnation of the universe you're watching. I don't think I like that idea, because I've seen all the disappointment, confusion, and fighting it leads to, but for better or worse, that's the way the company has set things up. It's a very risky gambit to put your investment eggs in a specific GL because they can be, and probably will be, sidelined at some time or another...sometimes for indefinite periods of time.