I almost always have difficulty identifying one 'favorite' anything, because there are so many different choices, and there are often so many I like.
That being said, when I read the thread title, one movie that came to mind is The Bachelor and the Bobbysoxer with Cary Grant and Shirley Temple. There are so many funny lines that you miss quite a few the first time you watch it, so the movie becomes even funnier with subsequent viewings (at least for me).
Two romantic comedies that make me laugh every time I watch them are While You Were Sleeping and Return to Me.
How about Space Cowboys? It makes me laugh, just thinking about it!
Mrs. C 
