the___is the most important fact to consider when selecting a credit card if you do not pay the balance on your credit card every month. APR, annual fee, late fee, over-the-limit fee

APR.

If you don' pay off your balance every month, you will pay interest on the remaining amount. The amount of interest is the APR, annual percentage rate. So, if you are going to be paying interest you want to make sure this rate is as low as possible!