Atleast in the US, Visa backed by a bank. 7 transactions per second versus 24,000 transactions per second. Banks are fdic insured and handle security for you. You might be capable of securing a private key that you actively use like a debit card number, but I'm not confortable with it and there's no way I'd let my aging parents near financial vulnerability like that with an 80 foot pole. As much as we all hate banks and all the bad they do, they provide necessary services.