Pulp Fiction was great when I first saw it as a kid, and about seventy-five more times after that, but recently when I have gone back to it I don't find it as charming. It's still one of the greats, but it hasn't stood the test of age.
Forrest Gump did bring me to tears, long weepy ones. There's something about the progression in this movie, it feels like it parallels the curve of life, from love to loss and ending with the next generation. Another of the greats, and I haven't seen it in a long time, so I'm not sure how it would stand up today.
I can't pick a favorite movie, but if someone asked what was the movie that had the biggest impact on me, it would be The Shawshank Redemption. The message of hope and freedom resonated with me to my core. It's one of those movies that every time I watch it, no matter what my mood or what I'm doing, even if it's just in the background, my focus becomes set other things aside to watch it. I don't claim it to be the best movie ever, but it might be one of the best ever, and it easily beats the other two on the list.