As far as prose is concerned, Twain is, hands down, the top dog, and only one of two American authors imposed upon students that I could actually read for pleasure. The other was Ring Lardner.
As a juvenile, which was the time I did most of my fiction reading, I enjoyed the Hardy Boys series, and the series billed as Alfred Hitchcock and the Three Investigators.
The Little House in the Big Woods was read to me in the third grade.
I think Laura Ingalls Wilder told better stories, and was a better writer than most so-called 'greats' dreamed of, but hers wasn't an indictment on Western society in general, or the American people in particular, or of Christianity in effigy like much of the heady and cynical claptrap billed as American masterpieces.
In my short stint as a high school English and drama teacher, after units on Twain and Poe, I told the students to leave their literature books full of elitist drivel in their lockers, and I introduced them to short stories from the anthologies I would check out of the public library and had fun reading.
(My class were the sweathogs, now called 'at-risk' students.)
I showed up at the school at 5am and ran the photocopier out of toner. They ate that stuff up.
Tons of great authors out there.