I ALWAYS check rock auto first, there have been times when I need the part right now, but when I can wait, I buy every from rock Auto. There catalog to look up parts is top notch( I used to manage an auto parts store).
They're prices are always cheaper than any of the other parts stores and if there is a problem they are quick to respond and fix the problem, either with a new part or a refund. Can't say enough good things about them???