Since my choices are Best Buy and Circuit City, I shop exclusively at Circuit City. I bought my desktop at Best Buy, with the salesman telling me that it was a Best Buy brand (VPR Matrix) and that if anything went wrong within the warranty period all I had to do was drop it off. It went bad within a month (hard drive failure), I went to drop it off and the service desk told me that I had to ship it to the manufacturer. When I called tech support to find out who the manufacturer was that I had to ship it to, they told me that they weren't allowed to divulge that information. This went on for 8 months. I finally called my credit card to have the charge reversed; it was the only thing that got their attention.
After it was finally handled I spent two weeks on the phone withh their customer service people. The ultimate result was that there attitude was that if the computer was fixed, there was no problem. Personally, I will spend more at Circuit City (although their prices are usually lower) rather than go to Best Buy again.