If you are talking about something that you watch at the cinema or on TV then you can say either as they mean the same thing. Although I would say that the word 'film' is a more British choice with 'movie' being more American. The word film actually relates to the material that the 'movies' used to be printed on. If you think about a long time ago when movies were stored in those big circular containers - the material inside was called film. That's why we say film today. As for using it, just use either - both are fine and understood by everyone :) Rob.

All the answers are correct. However, here in Hollywood, there is even a finer distinction. You will often hear actors/actresses refer themselves as a movie star, not a film star. This is because a movie is a film but not all films are movies. Some are documentaries and home made "movies".

Movie is American variant and film - British

I don't know which one is better.