Credit-card issuers relentlessly tempt you with new offers, even as they keep changing the terms of the cards you carry. All that makes it easy to end up with a wallet full of cards. While it's always good to have a backup for an emergency, sticking to one card will minimize the number of bills you pay and maximize your card rewards.

If you carry a balance: Get a low rate that lasts You'll find it easier to chip away at a balance if your interest rate is well below today's 14.1% average. A 0%-balance-transfer teaser is tempting, but you can owe fees as high as 4% of the balance. And if you can't pay it off within six or 12 months, you'll be left with the hassle of chasing the next offer. Skip the promo and opt for a low ongoing rate. The American Express Blue card (800-223-2670) charges 4.99% for the life of the balance you transfer.

If you pay in full: Get a rewards card you can really use If you don't carry a balance, make your No. 1 card a rewards card. You're squandering your spending power, though, if you earn miles when you rarely fly or you flit between two or three cards. Among today's best offers: The HSBC Direct Rewards card (800-975-4722) pays 5% cash back on gas, drugs and groceries, and 1% on all charges above $3,000.

By Kate Ashford, Carolyn Bigda, George Mannes, Walter Updegrave and Penelope Wang