Mine is Lost Highway. It’s one of the most amazing pieces of media I’ve ever experienced. It’s dark, surreal, and I still don’t know what it’s about for sure. I have my own interpretation, as do many others. Who’s right? We’ll never know. The film is a fucking trip. I highly recommend.
I have three that all vie for the top-spot at different times:
The Life Aquatic with Steve Zissou is usually my top. I love all the performances, the practical sets, the goofy CGI, and the soundtrack (especially the ending scene with the expert use of “Staralfur” by Sigur Ros). I also grew up with an absentee father and while I never really developed typical “daddy issues” over that, something about this aspect of the plot hits me (same with why I have a fondness for Tron Legacy).
The Beach is also up there. Not a great film, but a favorite. I caught it right around the time I started surfing and developing an itch to see the world. I’ve also read the novel several times (which is quite different from the film). It’s whole commentary on tourism-as-colonialism is brilliant.
Office Space might be the one movie I’ve seen more than any other. While it’s a great comedy, the performances are perfect as is the themes (though the ending is kinda lame and feels like the movie loses steam). I grew up hanging out among cubicles with my mom and every character is someone that I have met.