"Film" is more common in the UK, so I mostly say film for that reason. However, in my writing (and sometimes speech), to avoid repetition, I often alternate "film", "movie", "motion picture", "picture", and even "flick", because they all describe the same thing: A work created for the cinema.

One thing I certainly don't subscribe to is idiotic snobbery over the idea that "film" somehow refers to a more "important" work than "movie".