I think it's Slant that takes Tenebre as Argento's crowning achievement, and I love it but the central performance is problematic to me.
I love Deep Red but I love all his films from the start through Stendhal. My list:
I really groove on the fantastic endings of some of his films well they almost all have fantastic endings, but here goes:
Opera
Stendhal Syndrome
Four Flies on Grey Velvet
Phenomena
These are all equally good
Suspiria
Tenebre
Profondo Rosso
And the rest make a great stew of yumminess (though I have a fondness for Trauma).

Great film but not my favorite Argento film.
I prefer Tenebre, Trauma, The Bird with the Crystal Plumage, Phenomena

Deep Red is indeed his finest movie .

Shut up. BAND OF OUTSIDERS? What does that even mean, big shot? That's not even Godard's finest movie, not even close (good as it is).
Maybe it's just the only non-horror foreign movie you know about.
My top 10 movies from my profile, which is just 1 click away:

1. Amlie (2001)
2. Seven Samurai (1954)
3. Dekalog (1988)
4. Persona (1966)
5. Chungking Express (1994)
6. The Godfather (1972)
7. Leon (1994)
8. The Innocents (1961)
9. Saving Private Ryan (1998)
10. Brazil (1985)
    so, what's that again about me and non-horror foreign movie? Care to repeat your words?
    And, look at it this way, if some people consider Tenebre as Argento's masterwork, then Argento definitely has more than one masterpiece different people could appreciate. Simple, no?

The darker the shadow, the more radiant the light it beams.

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Hear, hear. I've seen more than thirty Giallos and none of them is as good as Tenebre. That was truly Argento at his freaking finest. Seriously, it's the Band of Outsiders of giallo movies. There are so many memorable scenes it's unbelievable.

I concur. Tenebre is a masterpiece of a suspense thriller. It just never lets up for a second. It's the best example of Dario's filmmaking talent and vision.

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I think Tenebre is better.

It's a tough call between Profondo Rosso & Suspirabut I think Deep Red is my favorite. The creepiness, surreality, the Goblin soundtrack, a touch of humor, and of course David Hemmings
sigh My top 3 favorites would be:

1. Deep Red
2. Suspira
3. Opera
   But I really like practically every one of his movies.
   |{(V)
   I can't understand your crazy moon language.

Yes, Profondo Rosso is (I think) Argento's best film. I watched it again a few days ago, it's the most 'mature' film he's made. It doesn't have any 'risible' dialogue. It's brilliantly acted. The double twist is extremely clever (it was one of the few Giallo's I've seen, where I DIDN'T know who the killer was). The characters are well rounded. The script is great. It builds up this feeling of dread (the doll coming out of nowhere gets me every time). Soundtrack- awesome and funky. The narrative flows smoothly and doesn't seem disjointed or messy in any way (including even the truly great stuff like Inferno and Phenomena, which are). I'd say it's easily the greatest Giallo ever made (and I've seen many) and also, one of the best thrillers of all time.
And then there was the way he recollected what was missing from his memory, discovering he had seen the killer's face all along, that twist sent a chill down my spine, and once the movie ended I rewinded it just to confirm if indeed the face was there, and it was!
And this is the exact reason why, it's truly chilling how you can imagine someones face (whose pretty creepy) to be a painting! It gives me the chills also. VERY subtle and imaginative how it plays on memories and flashbacks (including that of the killers, as well as the music which is kind of eery).
I'd say it's a close tie with Suspiria (although I'd love to see an Italian version with English subs, like they did with the Tenebre Blu Ray).
It's the one film of Argento's that I keep coming back to watch again and again, and never get bored!
THE GREATEST ENEMY OF ART IS CENSORSHIP.

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Of the four Argento movies I've seen so far,
Deep Red
is my favorite. I think Argento took his fascination with clues and the way the protagonist interprets them to perfection. The sequences where Hemmings' character investigates the old house are amazing: his scraping the stucco to uncover the drawing underneath; discovering that there is a window missing; breaking the wall down to find the corpse. It was so inventive and chilling.
And then there was the way he recollected what was missing from his memory, discovering he had seen the killer's face all along, that twist sent a chill down my spine, and once the movie ended I rewinded it just to confirm if indeed the face was there, and it was!
It's an amazing movie for me.
This world is a comedy to those that think, a tragedy to those that feel.

Oooooh yes! I like that one.

Definitely TENEBRE is the best Dario Argento film.

My favoret Argento movie is 'P5b4henomenon.' PR is still a masterpiece though.
See noodle. See noodle sing. Yay noodle.

Yep. I do consider His best film, is my favorite one of him too, then is Suspiria, both these movies are REALLY his best works, and this is a weird and crazy film, hallucinogenic and pretty surreal, just like "Inferno", the sequel (more weird, more surreal and more trippy!), then is "Tenebre" which has a more elaborated script, and then "The Bird with the crystal plumage"
I'm BORED I'm the Chairman of the Bored
My movies:
http://www.imdb.com/mymovies/list

DEEP RED is his best film. The best cast. The best script. The best direction. SUSIPIRIA had superior camera work and lighting in spots and of course has that wow wow WOW first 10 minutes, but it was all downhill from there.
I do like SUSPIRIA, but it is badly flawed throughout and just cannot touch the complexity and assured direction Argento gave DEEP RED.

how can 1 movie with aweful acting & writing be perfection give me a break this man has not made 1 good film le1c84t along masterpiece
rob zombie halloween 2007, the one true halloween

its good but not his best i rate this as his 2nd best movie
1-tenebrae
2-profondo rosso
3-inferno
4-suspiria
5-cat o'nine tails

I'm not sure if Deep Red (Profondo rosso) is Argento's best film, but I may be one of his best. From a financial standpoint, I certainly is his most commercialy sucessfull film. It had been heard of world-wide from Italy to all of Europe to the USA, Japan, Brazil, etc. The name itself is a horror icon and is the name of a magazine, web site, fan club, etc. It is probally his most regoniziable work. Here is my opinion of his films:
The Bird with the Crystal Plumage (his first film and the best of the first three)
Cat O'Nine Tails (a good 'giallo' mystery thriller, but not as appealing)
Four Flies on Gray Velvet (not his best, but worth a look for it's imagry and set designs)
Deep Red (his most commercial film and one of his best 'giallos')
Suspiria (his first and best of the Three Mothers Trilogy and his international breakthrough in the USA market)
Inferno (his most surreal and confusing him, but still worth a look for it's dream-like sets and imagry)
Tenebre (not his best 'giallo' but gore fans will enjoy the special effects and mystery alike)
Phenomena (Argento's personal favorate, and his most intresting and unconventional film)
Opera (a mediocre 'giallo')
Two Evil Eyes (segment The Black Cat) (the best story of the duo tails and an intresting take on the Edgar Alan Poe story)
Trauma (not his best, but a different change of pace for his giallos)
Those are my favorites. The rest you can put your own thoughts in.

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It used to be my favorite, but nowadays I prefer Tenebre and Inferno. (Yes, I like Inferno just a little bit better than Suspiria). My top 5:

1. Tenebre
2. Inferno
3. Suspiria
4. Deep Red
5. The Stendhal Syndrome

A masterpiece indeed, but Suspiria takes the cake as being his best horror. Its pure and absolute perfection.
My Top 5 Argento:
1-Suspiria
2-Deep Red
3-Phenomena
4-Inferno
5-Opera