Also, you're probably going to want to avoid most things made before 1965.
That's mean. I love nearly every western I've ever seen, particularly older ones. Dunno why it's my favourite genre, probably the escapist nature of it as a middle class Brit. How can you not love John Wayne films, like Stagecoach and The Searchers? I also recently saw The Big Trail, his first big role, it was quite impressive.
James Stewart Westerns are often a bit different, and it helps that he's an oustanding actor. There's one called Broken Arrow about an ex-soldier developing respect for and gaining the respect of the Apache tribe - it's based on historical figures.
I do love Leone. Once Upon a Time in the West used to be my favourite western but these days I think it's Winchester '73 (James Stewart again) which a very classic western in terms of appearance, but similar to Leone in terms of story (revenge, revenge, revenge,) - I fail to see what makes spaghetti westerns
so different. Another favourite, Day of the Outlaw, is visually outstanding and a thrilling story.
And High Plains Drifter is a lot of fun - very interesting. Dunno about "great" though.
The one that best fits your description is probably Day of the Outlaw. It's so bleak and really blurs the lines between goody and baddie a great deal. I think Robert Ryan makes an ace anti-hero. Only problems are it's black and white and made in 1959. But watch it anyway, please
