I also like that they have a "Geek Squad", that will drive to your house to service it (be sure to ask about cost). Assuming there is a Best Buy near you, you might like the low prices and the option of returning it if it's DOA, or fails during warranty...

FYI: since they are all pre-configured models, don't just look at the chip, but look at all the main peripherals (DVD/CDRom, card reader, digital video out if you have a good monitor, TV card if that's important to you) - what you want to compare between similar models, is which one has the more current add-ons.