I have an American Airlines credit card. Since my home airport is Reno, NV I don't have many choices of airlines.

I use the card mostly for upgrades to first class rather than for free tickets. So far it's worked well.

I looked into one of the Capital One cards that are good for any airline. The way they work is that you get a set number of miles/dollar spent. They are ONLY good for free tickets and can't be used for upgrades when you've already purchased the ticket. I called them to verify this.