Blood Meridian is also recommended as a revisionist Western, and probably better than Warlock (though that's a bit unfair as the earlier came out later).

All in all, both worth a read, if you have to choose:

• Blood Meridian if you are OK with some harsh violence and some "men are animals" narrative.
• Warlock if you want to read an honest effort in historic fiction for a town set in a period that is often aggrandized in our own mythology.

If somehow neither of these are interesting to you, there's also Butcher's Crossing, which is contemporary to Warlock, but a completely different novel (while still a big part of the revisionist western).

These three are called the greatest western novels (Iirc).