I sat the June 2009 administration of the LSAT. I started studying in mid-April by going through Princeton Review's Cracking the LSAT, concentrating mostly on logical reasoning and critical reading. I never took a diagnostic test, because I wasn't particularly interested in what my score would be with no preparation – the scores I really wanted to know about were those I could get after studying. After around two weeks of studying, I took two of the practice tests in the Princeton Review book, on which I scored a 166 and a 170. A week later, I moved on to my first official LSAC practice test, on which I scored a 179.
Good for acquiring a general knowledge of previously unknown material, however the Princeton Review book is required for more in-depth knowledge. Practice tests are much easier than the real thing.
Of the three, I find the Princeton Review book to be the best overall
Plus, the price of the book isn’t all that cheap. At almost $70, I’d rather invest a few more dollars to purchase the full Princeton Review Series books that comes with a total of 6 books. That and a lot more practice problems.