Buy this one!
I like this book. I work as an Exchange consultant and I use the book a lot, both as a reference guide and to get new ideas. I think the level is great, not too much "click here, click there" (just guidelines to good problem solving). I can definitely recommend this book, maybe not to the absolute beginners but for sure to every Exchange administrator with anger to take the system to a greater level.A great thing about this book is the comparison between old versions and the current version.Concerning the bad index someone wrote about, I know that was a mistake by Coriolis (the publishers) but all the books with a non matching index should be destroyed, if you got a book with a bad index from Amazon just return the book and get a new one.