1. As discussed in this Hub about travel rewards credit cards, the number one thing you want to consider is not if the card you're considering is the best airline miles credit card, but if it will be profitable for you! Consider the fees, rates etc. and sometimes, especially if you don't travel a lot, you'll find your card more to be an expense than a benefit. Of course, these airline miles credit cards have really nice benefits often, but be sure that the one you're looking at does it for you.
2. See where and how and when you can redeem your points from your credit card with airline miles. Very large number of points is not used up at all and just goes to waste.
3. If you get to a position where you have points on your airline miles credit card which are not spent you should know there are services (online) that offer you the option to spend them even if you don't have enough to redeem your airline credit cards bonus miles earned.
4. Don't get your credit card with airline miles and then spend money using it just to get enough airline miles for free. That's one of the worst things you can do.
5. With every card there are various bonuses associated, e.g. US Airways Visa Signature Credit Card has a $99.00 companion certificate you can get every year. Review these bonuses, they can add up to a lot and be perfect for your particular requirement and add really a lot to a card's value. There are probably no best airline miles credit cards, only the best one for you!

Airline miles credit cards can give you really nice bonuses if you get what's right for you. Enjoy it and good luck!