re: debit or credit

Debit is you personally guaranteeing payment to merchant while credit is a third party guaranteeing payment to merchant. If you have adequate funds in the account then the transactions should be handled the same since the institution issuing credit on your behalf has means for instantaneous repayment. It is only when you have inadequate funds when it should make a difference. What are the fees for overdraft protection versus the interest cost on borrowing, and what are the limits of each?