While we're at it... though it's not quite as good as the novel, I'd also suggest
True Grit (1969) and even
Rooster Cogburn (1975):
True Grit (1969) Rooster Cogburn (1975)
Not to mention, for a lighter touch,
McLintock! (1963):
McLintock! (1963)
(Not exactly a big John Wayne fan, actually -- nor am I a big opponent of him as an actor -- but the man
did make one heck of a lot of Westerns, several of which are definitely classics of the genre....)