Favorite of all time is difficult. There are so many variables that can change an all-time favorite. That being said, I'll put together my favorite(s) of all time and why. *** Disclaimer, my top 3 are purely based on personal choice, not necessarily on quality of story, cinematography acting etc.
1. The Big Lebowski - I love Jeff Bridges and John Goodman in their roles. The story is, meh but the comedy, drama and obscurity flow well.
2. Nacho Libre - Jack Black was phenomenal. It's a family friendly movie that people of all ages can enjoy and relate to. One of the most quotable movies of all time. The comedy is effortless.
3. The Thin Red Line - This is one of the only war themed movies that I've watched that dives into the psychology of servicemen. There is an ubiquitous amount of inner monologue that gives it's audience a unique view of the who the characters are, based on their thoughts, emotions and motivations and how it impacts their actions.
4. Tombstone - The drama is fantastic. The cast is superb. I've always been a fan of Val Kilmer and his portrayal of Doc Holliday was profound. His line about one of the antagonists resonates in me. "A man like Ringo has got a great big hole, right in the middle of him. He can never kill enough, or steal enough, or inflict enough pain to ever fill it."
5. Dune: Part Two - One could argue that I have this one on the list due to recentism, but they'd lose. The book series is my favorite of all-time (first three books), so there may be some sentimental value added, I'll give you that. I could talk all day about this movie, but I'll keep this as concise as I can without giving any spoilers (There are few things I hate and spoilers are one of them) and I'll only consider the merits of the movie, not it's representation of the book. First off, this is a must-watch in the theaters movie. Dolby Atmos, or whatever the highest audio quality and largest screen available is recommended. Also, you need to watch Part One first. Part two is a cinematic masterpiece. Masterpiece. The writing, directing, acting are all great. Those are the big three that people look at. Denis Villeneuve's ability to submerge the audience into the story is on-par with George Lucas' in the original Star Wars trilogy and I'd put this movie up against Empire Strikes Back. Yeah, I went there. Here's why - in addition to the writing, directing and acting (acting was better in Dune) the cinematography is unrivaled by any movie I've seen in recent years and the score is both eloquent and gripping.
6. Inception - I love the concept of this movie. The cast is amazing and so is the acting. I'm a Christopher Nolan fan and this is one of his greatest films. This is a thought provoking movie that, well, if you've watched this movie, you know what I'm talking about.
I could easily put half a dozen or more movies on this list, but these ones check the most boxes for me. Here's a list of honorable mentions, in no order:
Donnie Darko, Black Swan, Lonesome Dove (Not a "movie"), Empire Strikes Back, Arrival, Lincoln, Prisoners, The Departed, Forest Gump, The Breakfast Club, Goonies, Ready Player One, Tron: Legacy, Tommy Boy, Home Alone, Unbreakable, The Game, Castaway, Edge of Tomorrow and World War Z.