I think it depends on your level of expertise and if your looking for recipes, techniques, bbq history, dining locations, comp's or backyard? If you're looking for a book to help in comp's keep your money. None of them are going to come close to a class, mentor or experience. Most will give you the basics but not enough to come close to winning. That's just reality, no one is going to give you what you need to win for $19.95. If you're just starting out and want to learn the basics there are a ton of great references online (esp here). If you really want a book then pick one that will best fit your style whether it's hot/fast, low/slow or regional tastes. JMHO...
FEC120, XL BGE, DigiQ DX2, UDS, Cimarron, Weber Jumbo Joe, Grill Grates, ThermoWorks RT600C