Favourite films

The other day I attended a rather formal lunch here in St Andrews, and there were eight at the table. I didn't know any of the others but after a glass of wine and some bread we all got along just fine. They were of course most interested in the fact that I was teaching and studying film and after a while the inevitable question came. "So, what is your favourite film?". I can't answer that. My usual reply is "It used to be Rear Window but not anymore. Not because I think any less of it, it's just that I've seen other films which are just as good, or even better." And then I usually mention some titles I feel will be appreciated in the particular setting I'm in. What I mean is that I mention films that I think they will have some knowledge of. So if I'm for example asked by kids I mention other films than I would when asked by people in their late 50s. And I can do this without cheating because there are so many films I can truthfully call favourites.