Tough one for me. Let's see...as far as films go, I have a hard time thinking of something better than the Coen Bros. True Grit. It was well acted, the cinematography was excellent, and while not an exact copy, it stuck closer to the spirit of the book (which is fantastic, and should be read if you get the chance - it just drips authenticity).
For Television, it's a toss up between Hell on Wheels & Deadwood. Deadwood felt more authentic, and I think you'd be hard pressed to find a better TV western in terms of how it was shot, the budget, authenticity or character development. That being said, Hell on Wheels is just a ton of fun.
However, my number 1 spot might have to go to a video game called 'Red Dead Redemption.' The game is set in 1911, and follows a former outlaw who is being forced to track down and kill his former gang members. It was what got me interested in the Old West, and so I owe it a lot. One of those things that'll always have a special place in my heart.