Star Wars had the most impact on me for sure, and I never tire of it. It's also one of the few that I'd enjoy almost as much just listening to the audio, since the scenes are so ingrained in my head and I can practically quote the whole thing. I can just put it on while I work on some errands.

But I'd have a really hard time limiting my favorite movies to 10. My faves in no particular order:

OT, LotR trilogy, T2, Raiders, Last Crusade, Matrix, Inception, Aliens, Tombstone

If the list is expanded to include miniseries, then Band of Brothers is at the top, hands down.