Before Sunset
I believe this film is so perfect in every way.
Celine has been my favorite person in all of cinema since I saw the first movie two years ago, but my god. She's executed so well, and the last 20 minutes, in particular, were my favorite of the first two movies of the trilogy. That car scene, followed by the ending overall, was too good.
Initially, I didn't think I'd like it better than Before Sunset, which has been a favorite of mine for years, but these characters evolved so beautifully from what I knew of them. Every bit of dialogue never felt forced, and the creators never bent over backwards to make Celine or Jesse free from change or imperfection, even as they've progressed 9 years later.