I’m surprised (but very pleased) that you refer to Battle of Britain as a classic, I didn’t think it would have been regarded as such. I love both the Goodwin and the Walton, by the way.
I am sure within the UK it is a classic, maybe just not worldwide.
I primarily buy what I like and want to have. I like most classics becuase they are the classics I grew up with liking film music. Of course there are some I like more or less.
For example I generally love Herrmann but CITIZEN KANE or THE GHOST AND MRS. MUIR many consider top classics belong more to categores 2 or 3 for me. As PATTON was cited this is also not one of my top Goldsmiths, too.