There are so, so many very fine westerns. I picked out 23 whose content sticks in my memory and/or that I watch again and again. This list excludes spaghetti westerns. The ordering here has no significance. I think you can’t go wrong with these choices. I did not look at the list of 17 best westerns on the other web site, until after I posted this. I see rather low overlap. Their choices tend to be more of those conventionally chosen. Mine are more ones I really like.
1. Devil’s Doorway (1950)
2. The Last Hunt (1956)
3. The Law and Jake Wade (1958)
4. 3:10 to Yuma (1957)
5. One-Eyed Jacks (1966)
6. Yellow Sky (1948)
7. The Furies (1950)
8. Pursued (1947)
9. A Man Called Horse (1970)
10. Dark Command (1940)
11. Day of the Outlaw (1959)
12. The Hanging Tree (1959)
13. High Noon (1952)
14. Johnny Guitar (1954)
15. Mackenna’s Gold (1969)
16. The Man from Laramie (1955)
17. The Violent Men (1955)
18. My Darling Clementine (1946)
19. The Outlaw Josey Wales (1976)
20. The Return of Frank James (1940)
21. Roughshod (1949)
22. Stagecoach (1939)
23. Lonely Are the Brave (1962)
Tom DiLorenzo adds: American Outlaws.
Butler Shafer give a big thumbs-up to Open Range. See his comments.