I already have the AFE book for Nav (which my next and last exam), however I have just bought the Pooleys Nav book which seems more concentrated and according to an examiner at the flying school doesn't go off on tangents and concentrates on the material needed for the PPL exams and no more. It also says in the front it can be used as a guide for when you have passed exams and want to read back through.
It's smaller than the AFE books, so can be pulled out on the train, lunch at work a bit easier - i'm liking it but haven't finished it yet.