Price is the deciding factor for me, and I've rarely found an in store price that I couldn't beat on the net except for specials/rebates.
Honestly, I hate both of them, and when one has a great deal on something, I'll go to the other store & collect on the 110% pricematch @ the higher store.
Best Buy is irritating to me because of the lack of knowledge of their products & the long lines @ the service counter, C C is irritating cuz I can't think with a vulture hovering over me.
I've bought most of my appliances & big screen @ Sears, got ~$600 off my 61" Sony, free delivery & setup because I caught the right salesperson @ the right time with a quasi-legit price-match off the net, just bought a washer/dryer on sale the first week around $1200 with free delivery, went back the next week, & had them take 10% off because they had a Sears card promotion, then went back the next week & they made the entire purchase interest free for a year. (none of the promotions during week 2 & 3 had the washer/dryer as cheap as they were when they were on sale during the first week.) Best Buy had the models that Sears had rebranded for about 5% more. Try that kind of thing @ Best Buy/CC, & they'll throw you out of the store or arrest you...
The Sears I use is in a marginal part of town, so they have a lot of returned merchandise, I picked up a returned 5 burner smooth-top cooktop for $400, not a scratch on it, retailed for $785.