What's the Best?



I agree with the above posters. A book that's helpful for a master will be unintelligible for a beginner. Likewise, the best books for beginners are useless for masters because the concepts contained within are far too simple. Also, in my opinion the best books are ones that focus on one subject and explain it very well. Books which try to do everything end up being "jack of all trades, master of none". It would be better to ask the question this way:
What's the best book about: a) openings b) endgames c) tactics d) strategy e) thought in chess f) annotated games; for 1.beginners 2. intermediates 3. advanced players and 4. masters.
If there had to be only one book about the game of chess, (openings, tactics, endings, etc.), which one would you say would be the best, the ultimate, the book to put other books to shame? Keep in mind that this book should be easy to understand for all levels of players and yet challenging enough to make you think and reason beyond your current capabilities.