I have to go with Vertigo.
The script, while this is often not the biggest appeal of a Hitchcock movie, is unbelievably brilliant. It asks one question, from very early on in the film, a question that becomes more and more profound as the film progresses: Can someone dead possess someone living? It is a question that does not get rammed into our head once it has been brought up, but it is especially important to the growing obsession, and some would say insanity, that takes over him. The script is brilliant and flowing, and the characters are all brilliantly drawn, even if there are only really two big parts in the film.
The film's biggest success however, comes in the way it not only paints a picture of one man's unhealthy obsession, but in the way that it makes that obsession wholly our own, placing us within this character and this situation. We don't just see that Scottie has a terrible fear of heights. Through the magic of the Hitchcock Zoom, we SEE that he has a fear of heights. When Scottie first sees Madeline, we are in his perspective, watching her enter the room... the first time we see her, she is dressed in green, a colour that pops in the extremely red surroundings. The eye instantly is drawn to Madeline. Then, Scottie follows Madeline through the city, and we are often placed in his perspective. In one of the most brilliant displays of colour I've ever seen on film, Madeline walks through a flower shop, and we follow her. For ages, the film is quiet, almost silent, as Scottie pursues Madeline through town. When Scottie falls in love with Madeline, we fall in love with her. When Madeline dies, we experience pain like few ordinary films can make us experience. Because ultimately, unlike many films about love and loss, we are COMPLETELY entranced with Madeline, as much so as Scottie is. When Scottie experiences a nightmare about Madeline, it begins with an unfolding, animated flower. The flower shop scene earlier has worked its way into Scottie's subconcious, and it has worked its way into ours too. Through the dream, there are dazzling displays of green, of Scottie plunging into a literal sea of the colour. Scottie falling into it is a brilliant way of connecting his vertigo with his obsession. When we finally meet the real Madeline, we go into her flashback. Going into the flashback is the first time we begin to lose Scottie's perspective. It's an interesting and odd cinematic tool. For the rest of the film, we are distanced from him, no longer able to understand his now unhealthy and almost scary obsession. The film is beautifully shot too perfectly cue our eyes to every emotion. At first, I hated how the credits began, with a close-up shot of a stricken little girl. However, as we zoom in on the little girl's eye, the film's visual trickery becomes apparent. Brilliant, and easily misunderstood, intro.
The film is ripe with well interwoven themes and motifs, such as Scottie's vertigo and Madeline being represented by the colour green. The first time we see Madeline, as I said earlier, she is the only bit of green in a room that is wall to wall red. After Madeline dies, Scottie has a nightmare that is absolutely coated in the colour. As Madeline sits in the window, she is surrounded by green, a shadow within it. When we go into Madeline's flashback, we enter it through green light. Finally, when Scottie remakes Madeline into the women he remembers her, he waits, turned towards the wall, until she tells him to look. When he does, she is a spectre of green, too bright to be seen, until she steps out of it. Scottie's vertigo is brilliantly used, both as a symbol of his plunge into madness and love (are they so different?) and as a practical device. When he overcomes it at the end, we don't care anymore, since he's lost everything to do it.
The film ends on one of the most achingly tragic, almost echoingly painful moments in the history of cinema. As Scottie leads Madeline up the stairs of the tower, berating her, is he really attacking her for taking part in a murder, or is he attacking her for being remade by another man? It's the most subtle adultery metaphor I've ever seen. Finally, Scottie realises he's made it to the top of the bell tower, and has overcome and been cured of his vertigo. Then, Madeline leaps from the tower to her death, just the way she'd done the first time, and Scottie is left nothing to do but stare down several stories at her lifeless body...
A brilliant, almost artsy, film, that always respects our intelligence and never becomes pretentious, with a brilliant score by Bernard Herrmann, who also did Psycho.