Amazon is a store itself, as well as a portal for other stores to sell their goods. The product could be listed, but sold by another company.
Newegg is all in house. They have a warehouse of good that they sell from.
Another option is TigerDirect. Good store.
Best pricing is the thing you should look for. Newegg is the gold standard for computer components because they sell quality parts on the cheap, send out promo codes often, and have discounts daily.