J'onn has usually gotten along best with those Leaguers who are also aliens in some fashion.
Very true and a strong point of commonality between them. But they're also very fundamentally compatible even in the non-far-away-from-home ways; they're both very thoughtful, self-contained people who see and consider much more than they ever say, they both take after their mothers (second coolest thing Ostrander ever did), they're both very passionate about nature and the living world as a virtue unto itself. And they share the gift and burden of knowing, intimately, mankind's true nature, he through telepathy and she through the lasso; that level of empathy is pretty rare, and to have someone who gets it would be a relief to both of them.
In conclusion, Warlord.
You know, if you keep saying that, I'm going to have to actually familiarize myself with 4e.
Finally: congratulations on the voice acting debut!
rrgh don't say that it never happened i'm not here. >.>