With the help of a friend of mine - and I would like to thank him again this way - I have found that movie! It is LUNGA VITA ALLA SIGNORA! (LONG LIVE THE LADY!). In my opinion, it is a masterpiece. It is a great, excellent, magnificent, marvelous, fantastic, fascinating, superb movie! (I can't find at this time more superlatives, as I would have used them here, too!) The movie is perfect, from all points of view. It is mainly a comedy, but it has some dramatic elements also... and maybe a few horror ones, too. In fact, the movie is so perfect that it manages to convert little things like not having a lighter with you, at a given time, into a real drama. Also, the contrast between two worlds - the rich and the poor - is magnificently and uniquely achieved, mostly via visual means rather than dialogue, which is reduced to a minimum.
If, until now, somebody had asked me what my favorite movie was, I wouldn't have known what to say, as I had more than one favorite. Now, this "dilemma" is over, as I've got a clear answer: my favorite movie of all times is, indeed, LUNGA VITA ALLA SIGNORA!