Martian Manhunter - Experience with virtually every era of the League, the best set of utility powers available, and every skill any League COULD need.
Hawkman - The single most experienced hero in the DCU. Has access to virtually every skill on the planet, and amazingly advanced technology, such as the Absorbascon. Top tier melee combatant, extremely intelligent, and brilliant tactician.
Hal Jordan - Most experienced team player with the Green Lantern set of powers, thus netting him the power spot.
That is a really good top 3, even though I am NOT a Hal Jordan fan, it makes sense (I loved Kyle as GL).
MM really does need to lead the team and step into that, I think there are lots of story possibilities with that!