Completely disagree with you about Fierce Creatures, I loved that movie! The Brothers Grimm, on the other hand, was not (in my opinion) a good film.
I voted “Other,” for “The Meaning of Life”. Great skits, songs, production numbers… and a Grim Reaper who knocks Ingmar Bergman’s for six.
Plus it’s got the expensive, new machine that goes “ping!”. 
Monty Python and the Holy Grail is, AFAIAC, the funniest movie ever made. As my nom de Dope suggests, I’m a rather big fan of another great comedy troupe. But MP&HG is funnier than Duck Soup, Monkey Business, A Night at the Opera, or any of the other great Marx Brothers movies.
Life of Brian isn’t. It’s a good movie, but it’s quite clearly a movie about religion and stuff first, and a comedy second. I remember being disappointed by it for that reason when it first hit the theaters 30 years ago, and while I liked it better when I watched it again a couple of years ago, it’s still no Holy Grail. Part of that is that it isn’t trying to be, but the other part is that it’s neither fish nor fowl. It’s not a great movie when you set the comedy aside, and as comedy it’s far short of their best.
Unlike his bucket.
“Hoh dear. I 'ave trodden in M’sieur’s bucket.”
I’m in the same boat as many who are torn between Life of Brian and Holy Grail. I agree that HG is more quotable and has great jokes, LOB really drives the whole religion thing home. And, if you take it in all at once, it really is funny.
Holy Grail for me.
One overlooked movie is Chapman’s Yellowbeard. Not great, but some funny bits.
“Stager. Stagger. Crawl. Crawl.”
I vote Meaning of Life as the best, edging out Holy Grail.
I’ve never completely felt the love for Life of Brian. On an intellectual satirical level I think it’s brilliant, and definitely gets appreciative inward winks and smiles from me. But somehow, it just doesn’t delivery on the pure raw funny of their other films.
Add another Meaning of Liff fan here.
Another Holy Grailer over here.
I think both Brazil and Fish Called Wanda are brillaint movies, but they’re not really “Python” movies.
The Meaning of Life, for many things, but most of all the Universe song.
I voted for the Holy Grail, since that is the Monty Python movie. There are other movies on the list that I admire more as films (Brazil, for example) or that I’d choose to watch over that one at the moment.
Life of Brian, it’s the most cohesive and that makes the jokes work better, in my mind… not just wacky, random stuff strung together.
When I opened the poll and saw it open to peripheral projects, I thought for the briefest of moments about voting for A Fish Called Wanda. I almost wish I had now, it’s not getting nearly enough love. Kline and Curtis kill in it, and it’s my favorite Cleese vehicle.
Yellowbeard! I don’t understand why it’s such an unknown…
You’re problem is that you are an American, methinks.
In case you need some ignorance fought, allow me to over-analyse the background to the humour, and ruin it for you a second time:
In British public schools of the Monty Python era, all children studied Latin at school, from age 10.
The teaching method invoved rote memorization of millions of words. The first set of words were the nouns and matching adjectives ending with the suffix “-us”.
And , every single 10yr old schoolboy in England (yes, every. single. one.–no exceptions) proudly invented the most wonderful idea of all time, and told all his classmates about it, because , of course, nobody had ever thought of it before: if you added “-us” to common English words, then you could create sophisticated-sounding jokes! Try it yourself!!! It’s the funniest thing in the history of the human race!!! The whole school will think you are the best comedian of all time!! It’s unique! It’s original! It’s just wonderful!!!
For example, you could say … …“biggus dickus”!!! !!! !!!.
What–you think it’s not funny?..well, my dear champion, you should have tried when you were 10.
And after forgetting about it for a decade or so, hearing it repeated by adult actors on the big screen is,yes, very funny.
[/over-analysis] Carry on…
Oh, yeah --back to the OP:
The best scene in all of MPython for social-commentary type humor is:
the marketplace scene in Brian where the newly invented religion splits into rival factions immediately…(“follow his sandals…” …No…follow the gourd, the holy gourd of Jerusalem")
The best scene for the devoted-fans-who-already-know-all-the-best-scenes-by-heart is:
in Live at the Hollwood Bowl…When Eric Idle does his nonstop spiel as Mr. Smoke-too-much while walking through the audience.
I didn’t know that, although I was aware of the influence of Latin instruction on the graffiti scene in Brian. As an American, I find the Biggus Dickus scene funny in the context of being unable to laugh at the spectacular ignorance of a superior.
I also voted for The Life of Brian, as many othershave already said, it is the best Monty Python movie with a real story instead of a bunch of sketches strung together. I’m voting separetely from the related projects, if I included the related projects, I would vote for Brazil first, A Fish Called Wanda second, 12 Monkeys third.
Not to take away from Holy Grail, which is a rolling on the floor hilarious comedy.
Another vote here for Holy Grail.
We still quote it to each other, my friends and I, even after all of these years and gray hairs.
My favorite feature-length Cleese vehicle is the generally overlooked Clockwise. It’s a much “smaller” movie than A Fish Called Wanda, but it’s hilarious nonetheless, and it’s 100% Cleese’s show. It’s almost like a 90-minute episode of Fawlty Towers.