I used to enjoy browsing Radio Shack in the past, but now I am filled with a sense of trepidation as I approach the counter to buy. I am going to say that Radio Shack is the single worst customer service experience I have had in quite some time.
Best Buy offers the warranty, but it's not in a forceful, emotional sort of way like Radio Shack. The cashiers obviously aren't under pressure to push it. Of course, I hate the way Best Buy treats every departing customer like a criminal.
Walmart can have long lines at times, but in general it's fairly stress-free. Costco is awesome. The lines move fast and there aren't any pushy cashiers.