If you can, get both. Crisis of Conscience is more exposing the Watch Tower, and In Search of Christian Freedom is more about the doctrines and how many of them are not scriptural at all. I think both need reading more than once. If money is a problem I would buy In Search of Christian Freedom, and get Crisis of Conscience from your local library. In Search of Christian Freedom is a thick book [732 pages] and really needs to be around for references. Or maybe you could get both from the library, and then decide after you have read them if you wish to buy them for your own personal reference copies. (Beware the library versions may be old editions)
The latest version [2000] of Crisis of Conscience has quotes up to June 2000, so make sure you get that one and not an older version. (Amazon.com list it as 1999, but when mine came it was the second printing of the third edition, which was 2000)