Leone's spaghetti offerings are an interesting contribution to the western genre but I find them a bit overly dramatic and heavily stylised. Unforgiven is undoubtedly the best of the recent westerns.
Shane and The Searchers (one of John Wayne's better films) have already been mentioned as two of the greatest ever westerns and I'd add Stagecoach to that list.
I thought Unforgiven was one of the best because it reflected Clint Eastwood as an older actor playing an older outlaw or bounty hunter. Therefore the action sequences are not as frequent as they were in his earlier Western films. However, when they did come they were palpable and exhilarating.