You made me go look and analyse! It seems my top 5 are:Gollancz (57)Harper Voyager (54)Orbit (42)Corgi (23)Independents/self-publishing (18)then everything is quite spread out, especially the older books
From memory, Corgi used to publish Terry Pratchett? (So that'll have a few on my shelves too!)
I have no idea. I've never even thought about it.