Easy choice - Alien is cinema as art.

Both Ron Cobb's interior design and HR Giger's peerless biomechanical work emphasise the otherworldliness, isolation and claustrophobia of the premise (the latter also highlights the alien's role as a rape allegory, being a huge dripping dickhead with teeth). Jerry Goldsmith's score veers from sweeping classical to hair-raising experimental weirdness to nerve-shredding tension to hysterical madness, again perfectly complementing the story. Ridley Scott gives a shooting masterclass in every scene. Even the sound work.... Check out the scene with Brett looking for the cat under the landing gear. All those aspects combine there and it's absolute perfection.