I suppose we could discuss this, but to me the answer is easy: hands down, the best modern American novel I am familiar with is To Kill A Mockingbird by Harper Lee. The story of lawyer Atticus Finch and his children was published in 1960. It was supposedly based it on some of her own experiences growing up in Alabama. It is not perfect, but for what it is, it is awesomely good.
Today is Miss Harper Lee's birthday. She is 86 years young. So Happy Birthday, Harper Lee! And thank you for writing this wonderful book.
Harper Lee started work on several follow-up projects, but as of this writing she has not published any additional novels.
Ironically enough, another candidate for "Greatest Modern American Novel" could be Gone With The Wind by Margaret Mitchell. I wouldn't vote for it, but the ironic part is that it, too, was written by a woman and it, too, was the only book she ever wrote.
If you have never read this book, please go to the library and borrow a copy right now. You will not regret it. Then borrow the DVD version of the movie starring Gregory Peck. You will love that, too.
As a type of "trailer" I'll show you some different book jackets for this story. And I will also tell you that the title refers to one of the pieces of advice Atticus gives to his children: you can hunt and kill various things, but you should never kill a mockingbird. They only exist to sing and bring pleasure to others, so to kill one is a sin. And believe me, she writes that a whole lot better than I did. :-)