Get the 10th anniversary collection. There's a huge prologue where he writes about the inspiration and evolution of the strip and it's characters, as well as the conflicts he faced with syndication, his thoughts on licencsing and comic strips as a whole. The rest of the book is a collection of his favorite strips, and most of them have blurbs where he comments on their inspiration, fan/critic reaction, etc...from a single funny sentence to a whole page of backstory. It's a really wonderful book and is the most I think we'll ever get to hear his thoughts on the strip.
There's also another collection that showcases sketches and rough drafts of strips, but I'm not sure what it's called. That's actually the only Calvin and Hobbes book I don't have; I've got every other collection as well as the huge Complete edition they came out with some years ago.