Which pharmacy do you get your meds from? And what about mail order vs picking them up yourself?

I'm actually wondering if it matters where I get my BP meds from. Like, do cheaper generics have less effect or something? I see that Sam's Club and Walgreens have cheaper meds than my CVS pharmacy. (Well, any pharmacy has cheaper meds than CVS.) Does CVS have a higher quality or something? Or are they just overpriced?

Sorry for so many questions