I'd say it's a close fight between Napa and CSK (CarQuest isn't bad, either). I worked for our local CSK back in high school and was always satisfied with the parts I purchased for my daily driver (never had any issues with quality). So as strictly parts are concerned, I'd say Napa (premiums) then CSK. As mentioned, there are many stores who hire under-qualified employees, so it's always hard figuring out who has the knowledge to help you (EI: our local Advanced Auto is HORRIBLE!! for service/response speed).
I can't remember all the parts companies we used to deal with, but I know suspension parts at CSK are McQuay-Norris and are priced well for their quality. I'm not sure who actually produces Napa's Premium brand parts, but know their suspension quality is similar to Moog components.