I use a small independent pharmacy. (Why not? The copay's the same either way, and this way I support a small local business...) I'm not totally sure what the owner's primary business model really is, but I do know that he has great customer service and is willing to do things like home delivery of prescriptions or even staying open a little late for people to pick them up -- things the big chains would never do.
I've found different pharmacies charge different prices for the same drugs. Costco is usually cheaper than other pharmacies for identical items. I don't have a set copay for prescriptions it seems like. I don't get prescriptions filled on a regular basis either. Last thing I had filled was some norco when I broke my wrist 3 months ago*. Before that I don't remember the last prescription I had filled, but my wife had some norco for her dental surgery which happened 2 days before I broke my wrist. We went to different pharmacies and paid different prices for the same generic drug.
I've never been inside these pharmacies, it just strikes me as odd that a small business would be able to compete when costco, sam's club, rite aid, kroger, other small independent pharmacies, etc are all within walking distance of their location.
*I also had a prescription for motrin, but I asked for the price before filling it, and even though it was only a few dollars for a few pills it was many multiples over the OTC unit price for the smaller IBProfen.