Angels have the Phone Box
Hi Peter. I think, for purchasing, you want to try and stick with *one* reputable supplier. That makes things easier if you need to return stuff that arrives damaged or non-functional (yes, it happens). Then also, you always want to deal with a reputable place which has a very good return policy. Amazon is one good source, with competitive pricing, and an excellent return policy. I'm sure @essenbe will concur on that one.
The list from PCPartsPicker just shows stores with the lowest price at the time you put the list together. I don't go by that, except to get the total price estimate.