I think the only bit of Walton's score that made it into the Battle of Britain is my favourite - Battle in the Air? Wonderful music accompanying a great scene, both of which seem to capture what I can only imagine it must have been like, from the various accounts I've read from those who were there. To be honest, I'm not quite so keen on Goodwin's contribution though, too martial for my taste!
Mind you, the music at the start of Catch 22 is pretty choice too - just birds singing and the sound of Wright R-2600s starting up... magic!
Still, I'll stick with Battle of Britain.