As seen in the stupid movie thread, there’s a lot of opinions as to what’s stupid and what isn’t.
What movie can you come up with that could be considered the least stupid?
Most Hitchcock movies fit the bill.
There’s also The Usual Suspects and Shakespeare in Love
Well, wow. This seem like SUCH an obvious question, but I never thunk of it even after reading the thread you linked to. I guess that is what denotes genius. What an excellent question!
I’ll be thinking about this for days to come…but for now, one that does stand out is “Days of Wine and Roses” with Jack Lemmon and Lee Remick.
I know there are more; forgive me if I post again later.
Man, as much as I rant on about the stupidity, laziness, and just plain trash that they put in movies, this is a great opportunity to give credit where such is due. Thanks again.
Leone’s Once Upon a Time in America
Hmm. Define your terms. You mean the movie with the least stupidity in it? Like say Pulp Fiction or The Passion of Joan of Arc or Devil in a Blue Dress? Or, the most complicated movie, that requires a lot of concentration and participation to “get,” like Eyes Wide Shut or Last Year at Marienbad or The Cook, the Thief, His Wife and Her Lover?
(All totally top of my head titles; I reserve the right to go, “oh, I shoulda said The Magnificent Ambersons”!)
The Station Agent.
2001, a Space Odyssey. Written and directed by geniuses, and so smart the run of the mill reviewers had to see it twice to get it.
As few plot holes as possible - no storylines that are introduced but never go anywhere. If anything seemingly important happens, it should mean something (unless it’s a mystery or horror movie - red herrings are okay).
Consistency of established rules (see Star Trek for how not to do this).
…and so forth.
I like to think “Holes” meets your criteria. Everything ties into everything else.
I gotta go with 12 Monkeys
An excellent movie that unfortunately falls on the indie movie cliche that pot magically bonds everyone who smokes it.
I think The 7 Samurai is a pretty good fit to the OP requirements.
If your talking about the most realistic, it was probably one I turned off after ten minutes because I was bored to tears. (Reservoir Dogs?)
If your talking about the least cliches, it would probably be the first movie I saw that featured those particular cliches:
Pink Panther (Humorous chase scene)
Dirty Mary, Crazy Harry (Action movie)
Casabanca (Film Noir)
Gone With The Wind
Nevrending Story
Both follow the books pretty closely maybe thats what you mean.
Definitely Citizen Kane for a number of reasons.
Most recently, The Incredibles. Even the capes make sense! 
Shattered Glass.
Mindwalk, three people wandering around talking about physics.
OK, the realism is not really an issue (except that Robert Shaw was too thin and healthy-looking to ever convince me he was Henry VIII) but wonderfully well-realized and internally consistent and well-plotted with masterful dialogue:
A Man For All Seasons
Of course, it was from a play, which would account for most of the good bits. Anyway, this is one of the least stupid movies I have ever seen.
The Enigma of Kaspar Hauser.
Rosencrantz & Guildenstern Are Dead
By the criteria given, I think Uncovered does pretty well. It is at least rather tightly directed, even if it doesn’t appear so at first. Pretty much every scene makes sense.
The chess game isn’t the greatest, containing some questionable moves (and questionable divination of a situation’s ‘best moves’. The book it’s based on handles this a bit better). Compared to almost every other chess game in the movies, however, it’s way ahead.
I suppose movies like the already mentioned Mindwalk or even My Dinner With Andre are far from stupid, but they’re not exactly good as movies.
I think a great contender for generic ‘least stupid movie’ is Primer. Almost all the science/engineering dialogue (outside of a bit of mumbo-jumbo about the time/anti-gravity machine) makes sense, the actions of the characters make sense, and it feels like how something fantastic (time travel) might actually go down if discovered by two guys in a garage. It is extremely confusing, even deliberately so, and that kind of goes against it, but I think it is possible to pull an intelligible story out of it.