I'm not enough of a student of film to confidently pick Hitch's 3
best films, but I'd hesitantly say Rear Window, Vertigo, & North by Northwest, essentially for the reasons given above.
My
favorite films are somewhat different; Rear Window stays on the list, but add Rope and Psycho.
ROPE is my favorite, for me the most watchable of his films. John Dall as Brandon owns this movie, his smugness is palpable. As a viewer you're eager for him to be caught, yet you have a strange sense that a heinous act that audacious should be successful. Stewart is great as always, and Joan Chandler is a tasty little dish. As with Rear Window, the limited set forces you to focus on the characters and the flow of events, and the few key elements of the set (the chest where David's body is kept, the hallway leading to the kitchen, the slowly darkening skyline) are used to great effect. The transitions are handled well, and the story unfolding in real time works perfectly for me. Hitch's trademark playful ghoulishness, and the reaction from more staid guests, is fun, and takes a serious turn when David's worried father protests the whimsical discussion of murder. Just a treat from start to finish.
REAR WINDOW is the ultimate voyeur film, especially since it treats the voyeurism as a very human sense of curiosity rather than a pathology. Stewart is awesome yet again, and Grace Kelly is one of the most perfect female creatures to walk the Earth, aristocratically sexy, yet eager to take on risky work digging up murder implements or entering other's apartments. The microcosm outside the window is fully realized and interesting, and it's very easy to see why the laid-up photographer turns his eye towards the inhabitants. Detective Doyle and Stella are excellent secondary characters, and the denouement always makes me tense, even though I know how it's going to end. I think I like this film primarily because I also have voyeuristic tendencies, and the movie tells me that if I indulge them a) I'll uncover a murder, and b) I'll get a regal hottie like Grace Kelly.
PSYCHO appeals to my love of horror films. Along with the brilliant Peeping Tom (also released in 1960) this was the seminal psycho-killer movie, with psychological depth, genuine nastiness, prurient thrills, and terrific performances. The shock of the (till then) lead character's murder, the bird's-eye camera angles (Martin Balsam's murder still raises the hair on the back of my neck), mother's reveal & the swinging lamp, Norman's creepy final scene... one of the most perfect horror films ever made. Fuck you, Gus van Sant.
If you ever go to LA, take the Universal Studios backlot tour. It's a 3 hour tour of the various movie sets that still exist on the backlot, including Marion's cabin and the Bates house. We weren't allowed in the house, but we got to enter the cabin. I used to have a picture of me sitting on the edge of the tub where Marion got snuffed, but it was lost.

Honorable mention: TORN CURTAIN. A decent film with 2 great leads (Paul Newman and Julie Andrews), this film contains one of the finest murder scenes in film history. The murder of Gromek is drawn out and brutal, very realistic and rough, and the lack of music makes it all the more authentic.
SHADOW OF A DOUBT, a movie I saw for the first time only 4 months ago. Weak ending spoils a good film with some fine performances.