Suspiria may be his most well known, and it deserves the attention. The stunning first sequence alone is enough to recommend it, not to mention all the crazy and cool stuff that happens the rest of the movie.
One of the last films shot in beautiful Technicolor, Suspiria doesn't just bleed, it bleeds bright, thick, orange-red. The cinematography is dramatic, edgy, and inventive while the sets and locations are truly stunning.
This is the first of Argento's “Three Sisters” trilogy which was followed by Inferno, which also has an amazing set up and one of my favorite scenes in any of his films (the underwater scene with the dead body), but lacks the follow-through of Suspiria. The trilogy, if you believe the rumors, is supposed to be completed sometime next year. Let's hope the delays on that one don't spell trouble.
Over all, many critics site Suspiria as his best work and feel he never lived up to it, but as a fan who has seen nearly all of his movies, there is always something to cherish in each of them, despite their flaws. But if you want flawless, then this is the one to go with as it is totally deserving of its “Masterpiece” status.
Plus it boasts a soundtrack by Goblin (a previous – and actually the first – Brix Pick for album).