Obvious pick, but yeah. What's so special about it, what makes it so much better than other "classic" Westerns? The Wild Bunch, The Magnificent Seven, Ride The High Country, even other John Wayne films like True Grit and The Cowboys are all far superior to it in my opinion. Maybe it's the fact that it predated all of those films, but even Bridge On The River Kwai, which came out a year later absolutely blows it away.
Edit: And the portrayal of Native Americans in this film is laughably bad, but everyone knows that.