I feel that there are several things to consider here;
Firstly - Damn Good Writers. Films such as 'Breakfast at Tiffany's' by Truman
Capote, 'Cat on a Hot Tin Roof' or 'A Streetcar Named Desire' by Tennessee Williams, 'Bar Fly' by Charles Bukowski. Each of these films is beautifully written. The dialogue is thick with sub-plots and a quiet, but audible commentary on the socio-economic themes that are indicative of the times in which they were written. (Boom!)
Secondly - Quotability. Surely the film with The Best Film Dialogue should be highly quotable, so we have films like 'Clueless', 'The Blues Brothers', 'Anchorman', 'Mallrats', 'Gone With the Wind', 'Gentlemen Prefer Blondes'. Films that have been quoted to me and I have in turn quoted many times. I have more than once cited Marilyn Monroe's line 'Don't you know that a man being rich is like a girl being pretty. You wouldn't marry a girl just because she's pretty, but my goodness, doesn't it help?' However, I feel that one liners do not a movie make! There is also a tackiness to each of these films that, although I appreciate, stops me from naming them the BFD. Of course I shouldn't be so quick to dismiss the most misquoted film of all time 'Casablanca'. One of my absolute favourites, however, the dialogue is not outstanding and it is overshadowed by the superb cinematography. So we continue to.....
Thirdly - Naturalistic Dialogue. These seem to be rarer and are films that genuinely surprised me because you hear people talk to eachother the way that people actually talk to eachother. 'Superbad' and 'Bridesmaids' would be perfect examples. I saw both of these at the cinema, the first with an ex-boyfriend and the second with my best gal-pal, and both times I found myself laughing twice as hard as I laugh with most comedies of their creed. The '....with hilarious consequences' stock of comedy, which I love. But these stood out. 'Superbad' was the first teenager film I've seen where the teenagers talk the way that teenagers talk. This wasn't the trite, over-indulgent, language creating of films like 'Clueless', 'Juno' or 'Mean Girls'. This was just really damn funny! And I had the same reaction watching 'Bridesmaids'. That was the first time I had seen a film about a group of women where they actually talked like a group of women. They fondly took the piss out of eachother and had actual conversations rather than one woman telling another her issues and the second woman agreeing. This was NOT 'Sex and the City' and thankfully this film was not ALL ABOUT CARRIE BRADSHAW BEING UNABLE TO KEEP A MAN! If I whinged to my friends as much as she does, I doubt they'd be so nice to me! Can't get a man? Maybe you should GET A REAL JOB AND STOP BEHAVING LIKE A LITTLE BITCH!
Phew! Anyway, after all of that deliberation, I have decided to go for *drumroll, fanfare, big bloody banner!!!*
Eternal Sunshine of the Spotless Mind.
"What? That wasn't a nomination! Where was that on the stupid big list I just read?"
Well, for anyone who stuck around, my reasons are thus;
"How happy is the blameless vestal's lot? The world forgetting by the world forgot. Eternal sunshine of the spotless mind, each prayer accepted and each wish resigned." - Alexander Pope