This is a great question. There are many credit cards in each category, but there's also some overlap. For instance, if you're flexible about which airline you fly, some cards offer miles that you can also redeem for hotel rooms, car rentals, and more. It's also smart to look for a card that can save you some money if you travel oversees by eliminating foreign transaction fees.

There's also a category of travel reward credit card offers that focus on cash back or on other popular rotating categories. Discover is just one of many issuers that have cards that offer up to 5 percent cash back up to the quarterly maximums in rotating categories, such as gas, restaurants and more when you enroll each quarter.

Some cards are considered "gas rebate" cards, but again, these credit cards usually offer a gas rebate as part of a larger rewards program. Some rewards cards offers a cash rebate on gas as well as other rewards in categories that change throughout the year up to the quarterly maximum. To earn cash back in these changing categories you will need to sign up each quarter.

Most people think of airline cards as travel rewards credit cards. Many airlines have co-branded cards with credit card issuers. If you fly on a single airline, this is a way to rack up a lot of points. Many travel rewards credit cards will give you a bonus award for hitting a spending requirement, generally within three months. Then you earn additional points or miles for purchases made on the card as well as miles you fly with the carrier.

In general, don't spend much time worrying about the category of the card. Decide what type of rewards fit within your lifestyle. Then take a look at your credit score so you know for what cards you might qualify.

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