I'm factoring in the quality of the book (I do a full color comic book which would probably only find a niche market at this point), distribution/availability (like that company owned by amazon.com), any proprietory software you need to buy, price, etc.
I also used lulu after looking around. They don't have an "vanity" type fee. You only pay for what you have printed and customers can buy your product directly from lulu, so your money is never wrapped up.
I published a photo/history book and felt their quality was reasonable.
I like http://www.lulu.com
You can print a single copy, or as many copies as you want–unlike other publishing places where you have to buy a truckload of copies at the minimum.