Napa and Carquest both have quality parts.
Agreed, I tend to trust their parts more than the other stores. I've used a lot of Napa parts on my vehicles over the past several years as there's one about half a mile from my house, I haven't had any problems with their parts that I can recall. In my experience most reputable mechanics source their parts from either Napa or Carquest when not choosing an OEM part. Carquest seems to do so much commercial business that they don't even have much of a retail presence in a lot of areas...
Anyway I hope Napa alternators are good since I just finished installing one yesterday. They had a few different options in both reman and new, new ones jump up in price quite a bit, so I chose the "better" reman with a lifetime warranty, which was not much more than the cheaper option.
My options available locally were Napa, Autozone, or an "Ultima" brand reman from O'Reilly. O'Reilly is pretty new in my area and I don't have any experience with their parts yet nor have I head anything about them, Autozone I avoid like the plague, so I hope I made the right choice.
I found some "new" alternators for very appealing prices online, but a couple of the reviews claimed the units people received were clearly remans and not new, and it was unclear if they were being sold with a warranty or not. I decided to pay a little bit more to get one locally, thinking that if I ever need to warranty it, it should be a lot easier to walk into Napa than try to warranty an alternator through the mail (which would probably take weeks, and the return shipping alone would eat up any money saved on the initial purchase anyway).