Which one? I have been in socal markets that have as many as seven competing yellow page books, which come out at different times (and some multiple times per year). Unless you have bullet-proof data for the business type you are running, you will have no idea what kind of sales/cost you will realize, and may have to go with multiple books. Some smaller books have incredibly high sales/cost in some markets for some businesses. A lot depends on your positioning, too, which is generally seniority based for each ad size. Having gone through this in numerous markets in a very YP-reliant industry, I would avoid YP if at all possible. When was the last time you looked for something in the YP?