Tv show - Deadwood . Although it could be pretty despressing watching at times.
Movie - Treasure of the Sierra Madre. Easily the best movie set in the 'Wild' 'West', although for another more traditional cowboy film then Good the Bad and the Ugly is brilliant, and (unlike many movies) very re-watchable.
Actor - Lee Van Cleef. Helped make the 'spaghetti' westerns as good as they were and a great foil for Eastwood's good-guy characters. He was a great actor, and unlike some, was equally adept at playing good or bad people.
Westerns are arguably my favorite movie genre and I just can't bring myself to choose.
Now obviously there are some I think are better than others.
She Wore A Yellow Bandana (really, I liked all of John Fords calvary trio)
The Good The Bad and The Ugly
The Sons of Katie Elder
True Grit (both of em)
Dances with Wolves (if you count that)
Actually, this is pointless as I feel I'm just listing them, lol I honestly can't decide after seeing probably more than a hundred..
A list of what I don't like would be much shorter than what I do.
For modern it would probably be tombstone.
For some reason, I have yet to see lonesome doves and The Man Who Shot Liberty Valance.