I loved Stacy Schiff's prize winning Cleopatra biography, and I live in Salem and have read a bunch of trial related books, but I found her "Witches" book very dry and difficult to get through, although it did have some interesting new information regarding some of the accusers and their standing within the community, and how this related to their accusations and those they accused, and how it wasn't necessarily a simple case of accusers = villains and accused = victims. If you had already read a bunch on the trials and were looking for even more exhaustive information, I think "Witches" was worthwhile, but I wouldn't recommend it as a first book to read about the trials.

Personally my favorite book on the trials is Frances Hill's "A Delusion of Satan: The Full Story Of The Salem Witch Trials." I found this to be the best combination of a comprehensive historical overview and readability; I found this book very hard to put down, the opposite of Schiff's. After that I recommend reading "A Storm of Witchcraft: The Salem Trials and the American Experience" by Emerson Baker, which looks at the trials in a larger context of early American history and Puritanism.