I don't think banks would disclose this type of information, since it would be proprietary business information and they wouldn't want to tip off their competitors about what cards are successful. However, from anecdotal observations at shops and restaurants, I would say that most people use debit cards, and most credit cards are the basic rewards variety, such as the cash back cards from BofA or Capital One, rather than airline miles or points. If I had to take a completely wild guess, I would say that the BankAmericard line is the most popular credit card in Southern California.