Ah, yes. The eternal questions raised by Haka secret actual personality which is barely hinted at in his cards.
But I think this one's still pretty clear. Paul heads up the premier super-team. Not only is he well-known to the public, but his family have been paragons of Amircaness since forever. And he's the one who, should he falter, the entire world's balance of power falls apart.
Haka is just a centuries-old nice guy. He might function as a mentor to Paul himself, but Paul is the lynchpin that holds things together.
The Scholar keeps to himself. Fanatic cuts such an imposing figure, the other heroes call her "Fanatic" against her wishes. Tachyon is awfully glib and big on the "for science" attitude, though she might grow into a more unifying (heh) figure in the future. The Adept* does not have a single quote or piece of card art I can think of showing a "morality" outside of "fight bad guys, talk about cosmic stuff" - I don't think he's a bad person, but I don't think he's really thought about the "big picture" enough to much of a moral paragon.
Bunker and Tempest, however, both seem like guys I'd like to talk over tough issues with (Bunker as a small guy who excelled in the army, then stepped up to fight supervillains despite lacking powers, and Tempest as someone who keeps working to save two races, neither of which have treated him well). They're not showy in the way that Legacy is, and they don't have the saintlike qualities Christopher talks about Haka - they would not fill such a grandiose title as "moral center," but for that very reason, they're the ones who I think would have the perspective to help with nuanced choices, while the bigger men are good for inspiring you to keep on going at all when all choices seem bleak.
Ironic
* As an aside, AA is older than Unity, Visionary, the Wraith, Expatriette, Nightmist, and maybe Fanatic - nearly a third of the other Hero decks. He is - barely - the youngest male hero, but since SotM doesn't like a lot of overlap between male and female age ranges, that still only puts him in the middle of the pack overall.