I say Batman
I’m tempted to be a jerk and say Martian Manhunter.
But my actual answer is Batman.
King of the sea and when he is not there The Queen
Depends what league specifically.
Hard to decide between bats and Hal
Like LEXC0RP said, it depends on what flavor of league is being discussed.
A few I like:
Post-Crisis JL: Booster Gold
Justice League Task Force: Martian Manhunter
Pre-JLA: Bloodwynd or Blue Devil
JLA (Morrison): Superman and Kyle Rayner
JLA (Kelly): Plastic Man
New 52 JL: Superman and Wonder Woman
The Flash (Barry Allen)
Awh, who am I kidding? Is there any question? Superman of course!
Superman/Batman, I love them equally, Wondies is a close second.
I would probably have to say Batman; his slice of the DC universe holds more of my favorites than any of the others. That said, I think I actually own more Green Lantern (Hal) specific comics than Batman (Bruce) specific comics.
Out of those choices Wonder Woman
It depends on what incarnation of the league.
All-time favorite, any incarnation, Stargirl.
More standard JL continuities, Wonder Woman.
Given Booster Gold is not on there I will have to go with my hero Superman.
Silver Green Lantern
Satellite Green Arrow
JLI Martian Manhunter
Zero Hour Flash (Wally)
New 52 Aquaman
Rebirth Martian Manhunter