I need to choose a book for my American Lit. class?

I have read The Help and Unbroken, but I have not read The Law of Nines. The Help can be a little dry at first, as most modern books, but once the plot picks up it can get quite interesting. Unbroken is a very interesting history book about the United States in the Depression/WWII era. The plot and themes are very interesting but the book wouldn't be for someone uninterested in the subject matter as it can be quite a bore if you do not like history. I can't really comment about the Law of Nines since I haven't read it, but between The Help and Unbroken, I would choose Unbroken because I am interested in history and such. Also what was the criteria of the books you had to choose. I know American Literature, but is there a specific time frame or list of books? I could recommend some great American Literature.