Definitely Twain and it's not even close. Huckleberry Finn even has the episodic flavor of The Odyssey.
For books you have "The Innocents Abroad", "Roughing It", "The Adventures of Tom Sawyer", "A Tramp Abroad", "The Prince and the Pauper", "Life on the Mississippi", "Adventures of Huckleberry Finn", and "A Connecticut Yankee in King Arthur’s Court".
That's a hell of a lineup and includes a LOT of the flavor of the US as a young country.