The first part of that duel isn’t especially memorable, but you’re right: after he pulls the knife out, it’s pure gold.
The backstory there, of course, was that Harrison Ford really needed to use the toilet so he ad-libbed a shortcut.
BTW, my suggestion is the barn-raising scene from Witness.
The hotel scene in No Country For Old Men:
Also, the first coin-toss scene. Can’t choose.
I debated posting here but I decided to start a new thread to talk about best scenes from television here: https://boards.straightdope.com/t/best-scene-in-television/1006483
I don’t know if it’s the best scene, but it’s the best music ever in a movie.
Yeah, I was late to that movie, but I really liked it when I saw it. And that was one car chase I actually watched (usually they bore me).
The opening scene in Once Upon a Time in the West.
The opening scene in Patton.
Just re-watched this because it’s just that good. At the end, there’s a radio voice saying something about the the 710 (I hate the 710), and I swear it’s Wendy Malick’s voice.
I surprisingly loved this movie. Surprising, because I came to with no preconceptions, and it went way beyond what I might have expected. Anton Walbrook was also so much better in the British version of Gaslight than Charles Boyer in the US version. Overall, I much prefer the British version.
I adore The Fisher King.
All of the “are you feelin’ lucky punk” scenes with a dash of “go ahead….make my day”. (And yes I’m pro-gun control)
It happens early in Dirty Harry, so that when Harry gets in a shootout at the end, everybody is couning how many times he fires. It is five, so he has one bullet left when Scorpio reaches for his gun.
But having seen the movie multiple times, Harry does not fire six times in the first gunfight, but he’s still out of bullets when he bluffs the bank robber. I don’t know if the fiilmmakers were lazy, figuring no one would bother counting shots, or if it has been edited for TV.
Morricone’s “Ecstasy of Gold”. I agree; it’s the best track of the best movie score ever.
I’d say any of the scenes in “Little Big Man” with Old Lodge Skins.
That was nice but I loved the very first shot when that Imperial ship (with SO much detail) flies over the camera for what seemed like days.
Maybe he had fired his pistol earlier and hadn’t bothered to reload. Also it was (is still is?) common for anyone carrying a revolver (going back to cowboys) to leave one chamber empty for the hammer to rest on safely.
The opening sequence from Contact.
The car attack scene from Children of Men.
The opening scene from Silverado (especially the last bit where Scott Glenn’s character opens the door and reveals that spectacular vista)
I remember a TV show where a Mafia hit man was quoted as saying the el rumble in The Godfather was spot on. He heard exactly the same noise inside his head whenever he was about to whack someone.
One of my best scenes in film is Ilsa’s entrance in Casablanca:
A six-foot-tall Nordic goddess strides through the door on the arm of a sophisticated Continental gentleman. She and the piano player recognize each other as she silently walks past, and right away you know we got trouble!
I think I prefer the crying scene in the refugee camp, but this is a good choice too.
Oh, yeah! I was seeing the movie for the first time after hearing about it for weeks, and I thought I had died and gone to Heaven! 
I saw that movie when it came out, in an older downtown theater in Washington State. I was stationed at Ft. Lewis and my parents were in town while on vacation. My dad had been stationed there in the early 50’s, during the Korean War, and had been in this theater many times. He wanted to see a movie, any movie there. So we waited in a LONG line and Dad, Mom and I saw Star Wars. Not #4, not A New Hope, STAR WARS. And that scene of the endless ship passing literally had my jaw dropping.