Yep. I use Discover first, M/C as a backup. Doesn't AMEX require you to pay the balance in full each month? I've heard or read that before, and always wondered how they make a profit. Is their only revenue stream the membership fee?
Some of their cards are like that. Others are more like traditional credit cards. I have an Amex Clear card that allows you to carry a balance, not that I do though.