It used to be easy. Old school FCP Groton for everything. Now, the process becomes analysis paralysis as I compare prices and shipping costs between Amazon, Tasca, FCP, and Rockauto.
Rockauto always has the best prices but the shipping charges from all the different warehouses can add up quick, making it cheaper to buy from elsewhere.
FCP usually has decent prices and free shipping. UPS ground gets it to me in 1-2 days, and their free shipping is 3-4.
Amazon almost always is the most expensive, but sometimes it makes sense with Prime shipping.
Tasca consistently has good Genuine part prices, little cheaper than FCP.
Oh, I remember fondly the days of the old school FCP website. And their hole-in-the wall brick and mortar shop.