Toss up between Thoreau and Twain, who will always have a special place in my heart because Tom/Huck were the first novels I read, about the time I started school, beginning an annual tradition of TomX2, HuckX1 every summer. The only thing sadder than Tom trying to turn his friends into Robin Hoods Merry Men is me trying to turn my friends in into Tom and his friends. Thoureau's just so darn deep though, and a personal hero; much more honorable than Emerson: "This is what I believe more than anything else, but I'm not going to do it, and will try to stop David from doing so either." Jerk. Thoreau may have spent a night in jail, but Emerson was in there his whole life, refusing to come out of it.
Jordan's in there somewhere, and of course Kerouac, another personal hero. We could all do worse than to fall in Love with God (hey, it's on topic, and it's the end of the Dharma Bums; what can I do?)
Hawthorne, he makes Emerson look liberated; bleah, I'd rather discuss Blake. Each to his own, but that's not American either.