The Empire Strikes Back. While Star Wars blew my then-twelve-year-old mind, and led to a lifelong fandom for me, the second film took everything that the first film had done, and made it even better.
Nearly 40 years later, if I’m in a down mood, I put ESB on, and it makes me feel much better.
I considered it. 
Blue Velvet. PABST BLUE RIBBON!!!
Dr. Strangelove, but a close second is Aguirre, the Wrath of God
Spirited Away.
There are a lot of great movies, but if I have to pick one it’s probably The Right Stuff.
I just saw it again on TV a week or two ago. All the action and adventure moments are great, but I’d forgotten how sweet the scenes with Ed Harris and Mary Jo Deschanel are.
Casablanca - a movie where great parts add up to a great whole.
The movie that I will watch any time and is absolutely the most quotable fun movie:
The Castle
This Australian “mockumentary” is 1. not long (80 minutes), 2. makes you happy, 3. doesn’t go for the turn to the camera laughs like Christopher Guest movies, and 4. has more call-backs than Arrested Development. I promise you’ll enjoy it the first time and it gets better every time after that. The U.S. cut/version is superior to the Australia release.
“Dad reckons fishing is 10% brains and 95% muscle, the rest is just good luck.”
“We’re going to Bonnie Doon”
“Tell him he’s dreamin’”
“Seasonin’”
“This is going to the pool room”
“YOu know what they say about Greeks”
It’s just a good fun movie about underdogs who you don’t need to feel sorry for.
But I do love “Goodbye, Mr. Chips” a lot too. Primarily about how it is an epic journey all in one place- using time and events to tell a crazy long story of a life.
Sweet Smell of Success
“From now on, the best of everything is good enough for me!”
The one movie I’ve re-watched the most in the last 15 years is Sideways. But…I watch it with the commentary track. It’s great fun to watch Jack the jerk and Miles the sad sack fumble their way through a bachelor party weekend while listening to Giamatti and Haden Church crack wise about the goings-on.
Runners-up for favorite movie would be Contact, Paul, and Moonlight Kingdom.
Airplane!
The funniest movie ever made and my favorite movie of all time.
Also, only on this message board could a single-answer question be answered with so many multiple answers and caveats 
Great flick. After all these years, “tell him he’s dreamin’” causes an immediate smile, and brings back all the hilarity and warmth that movie has to offer.
I’ve already named my favorite, upthread, but reading the choice made by posters tells you something about they themselves. I started listing the films here that would be on a “top 20” list for me and came up with nine. All of them are very different films. Then I added others not mentioned here, and I’m up to fourteen. Maybe I’ll start a thread like that.
No matter how many times I see it or think about it, Miles’ line
“I’m not drinking any fucking Merlot”
always kills me.
Good to hear, I wouldn’t have replied if you said the remake, but I would be wondering if you had a serious head injury. 
Arthur is a very good movie, I still use Hobson’s “I’ll alert the media.” from time to time, though no one seems to know it anymore.
Interesting the range of movies being cited!
Also interesting that at least a few Dopers have handles or quotes from a movie, but cited a different movie as their favorite.
Finally, interesting that I am the first to mention…
Big Trouble in Little China.
“We really shook the pillars of Heaven, didn’t we, Wang?”
If the question had been best I probably would have gone Valley of Gwangi but ------- there is something in Dinosaurus! that always just appealed to me more. The human acting is a little better and the little boy with his cereal toys -------- it just has something. And the caveman while funny is also a little heroic as well. Ray did stop-motion the best; he is without the best that ever will be since CGI has basically killed a lot of the art. But Dinosaurus! just has that “it” factor" for me.
Now if we were talking Christmas movies ------ Santa Claus Vs. the Devil. What can I say? Stories, even bad stories, are just my thing.
What Ever Happened to Baby Jane?
Die Hard
Casablanca is the one I’d take with me going into exile.