The Wild Bunch.

Nevada Smith.

3:10 To Yuma, the original with Glen Ford and the remake with Russel Crowe are both excellent. Original story written by Elmore Leonard.

The Magnificent Seven. Watch it with The Seven Samurai.

Once Upon A Time in the West.

True Grit, original and remake.

Blazing Saddles.

The Naked Prey. Movie takes place in Africa, but it's based on a true story of the American West. https://en.wikipedia.org/wiki/John_Colter#Colter.27s_Run https://en.wikipedia.org/wiki/The_Naked_Prey

https://duckduckgo.com/?q=best+western+movies&t=canonical

Any comprehensive study of the genre must include movies directed by John Ford; and movies starring John Wayne. There will be much overlap in these two sets. Wayne was not a versatile actor, but any study of The American Western without significant attention to him would be incomplete. "Stagecoach" and "The Searchers" are good examples of their early and later collaborations, respectively. Howard Hawks' "Rio Bravo". Anthony Mann's westerns starring James Stewart. More recent suggestions would include Lawrence Kasdan's "Silverado" and Clint Eastwood's "Unforgiven".

Tombstone. I didn't mind Django: Unchained as a riff on Westerns.