I started out with the book, and read it twice. Not bad for someone who doesn't like to read. When the CD set was available I bought it without thinking twice. I have a 1 hour commute into work, and every once in a while I put the CD set in the car and get a GTD refresher. The CD set is very entertaining too. A lot less work than reading for me, and makes good use of my commuting time (well, not as good use of my time as listening to Metallica!).