If you want to find out more about Dianetics and Scientology, the best way to do this is to read an L. Ron Hubbard book on the subject. I personally recommend you read Self Analysis.
Living a better life, however my daily life is not characterized by the favorite book. It is the long row of all the different books, tapes, course packs that counts. Being able to grasp the relevant data to the day to day questions is the real force of Scientology books.