There are a lot of good ones so picking ONE won't really be possible. I'm a fan of Weber's "Smoke", Dr. BBQ (Ray Lampe) "Slow Fire", and most recently, Myron Mixon's "Everyday Barbecue" is looking pretty good. I also have Chris Lilly's "Big Bob Gibson's BBQ Book", Myron Mixon's "Smokin" (which I don't care much for), Adam Perry Lang's "Charred and Scruffed", and several others. Weber's "New Real Grilling" is on my to-buy list...
Kamado Joe Big Joe ° Kamado Joe Classic ° Old Country BBQ Pits Brazos Offset
UDS ° Traeger Lil' Texas Elite