SInce this subject never comes up and google doesn't have any results either, let me add that I've been using Seeedstudio since year 2009. Very happy with the quality of the boards, options, and price. They only test 5 of the 10 boards, but I have yet to find a failed one.
My only dislike is all boards have to be retangular. Some services will route shapes for you, Seeed does not.