Depends on your goals, or if it's a gift for someone else, their personality.
These are my favorites:
Paleo Solution by Robb Wolf.
Practical Paleo by Diane Sanfilippo
Primal Blueprint by Mark Sisson
Paleo Answer by Lauren Cordain
Perfect Health Diet by Paul and Shou-Ching Jaminet
New Evolution Diet by Arthur De Vany
Wolf's and Cordain's books are best for those who are more interested in the science, Cordain's for those that wouldn't enjoy the fun snarkiness of Wolf's book.
Sisson's book is for those that just want a quick start without too much science.
Sanfilippo's book straddles both of the above categories and covers material that they don't.
While the Jaminets' book is considered "high carb" by some, it's actually very low carb when compared to a typical SAD diet, and covers materials that the others don't.
De Vany's book is shorter than the others, but covers interesting topics in working out that the others don't, specifically, that you shouldn't do the same thing over and over again, not just in terms of workouts, but also diet. Applying a fractal approach to living is far more beneficial because you don't constantly stress the same pathways at the detriment of the others. For example, by not eating just chicken breasts and broccoli, you don't constantly stress the same detox pathway; By not doing the same workout over and over, you don't hit a plateau and convert fast twitch muscle to slow twitch. His video lectures are probably even more valuable (but read the book 1st).
I used to be subscribed to his pay website, which admittedly had a lot of interesting articles, but before I decided to not renew, the posts of mostly "another marathoner died of heart failure" and "here's what my dinner looked like." Not sure if that's changed or not, but I may renew again if I see he posted interesting things again. He's got a nice forum, but nowhere near as full of life as paleohacks.
They all bring something to the table, and almost all are suited for beginners (again, with the focus on the readers' personality, plus different topics.)
Although I've not yet read it, but it's in my kindle, Dave Asprey's Upgraded Chef may turn out to be a decent book just based on his podcast, blog posts, and presents a different way of looking at paleo. (His intro to this version shows spectrums of food and other things where the more you stay to the green side, the better off you are.)
That is a tough one. Both Primal Blue Print and Paleo Solution are good. That said, unless it is a gift for a friend etc... I think the websites are better than the books, more info and searchable.
I would have gone with Primal Blueprint right up until my copy of Practical Paleo arrived. This book is absolutely fantastic. It's got everything in plain English, many meal plans for different types of diets (fat loss, high blood pressure, etc) and lots of fabulous recipes. I just bought it for my brother-in-law and he loves it.
I'd be tempted to wait for the 2nd edition of the Perfect Health Diet coming out December 11, 2012. The Jaminet's are amazing at summarizing all the science literature and evidence.
It probably does depend on the person, though. The basic info is pretty similar and varies a little with things like dairy. Back when I read The Paleo Diet (classic), Primal Blueprint, and The Paleo Solution (style of humor most like and some find off-putting), the Primal Blueprint was most enjoyable for me. And Mark Sisson's website (author of Primal Blueprint) is a fantastic resource. I think it helps to have a good ongoing online resource after reading a book. Then I read the Perfect Health Diet and the evidence-based style makes sense for me.
I haven't read Arthur De Vany, maybe because he's had a membership web site, instead of more open.
I haven't read Practical Paleo, but other commenters have me interested ...
This would not be my 'one book', but try "Chez Panisse Vegetables" by Alice Waters. Seriously. Tons of the recipes are paleo, and it'll teach you great cooking techniques that respect and highlight the flavors of fresh seasonal vegetables.
While meat's easy to like (and gets most of the attention on these boards), side / vegetable dishes are often where paleo cookbooks come up short. This is a great resource.
Robb's book was the one that started it for me, and for a new to Paleo person, this is what I would recommend. However, I want to give a shout out to Balanced Bites' book Practical Paleo. For someone like me, who's been in this Paleo thing for a while, it's my choice for favorite book. I love the info she gives (it's like taking Paleo to the next level), the meal plans and the recipes.
Hunter/Gatherer Book Recommendations 9 Answers