WITH SO MANY CREDIT CARDS

offering rewards programs these days, the question for many card users is no longer

to use a rewards card, but which one to pick.

For people who carry a balance, the No. 1 priority should be to find the credit card that offers the lowest possible interest rate, or annual percentage rate. But for those who pay off their balance in full each month or who carry a balance but can get a competitive APR from a rewards card rewards programs are the rare situations in life when the lunch is truly free.

So which is best? Rewards programs can vary widely in terms of how quickly you can earn points and how many points you need to redeem a reward.

We decided to look at the four largest and most popular rewards programs: American Express' Membership Rewards, Citibank's ThankYou Network, MBNA's WorldPoints and Visa's rewards program for debit cards, Visa Extras. Unlike other rewards programs that tie your card to a single brand or merchant, these offer a wide choice of rewards, including travel, merchandise and gift certificates.

We'll be honest: We can't pronounce a clear winner in all areas. Citibank and American Express, for example, came out a step ahead of MBNA and Visa Extras in terms of generosity. (You need 10,000 points for a $100 gift certificate from AmEx or Citibank, but 13,000 points with MBNA and a whopping 40,000 with Visa.) On the other hand, the Visa Extras program doles out loads of bonus points.

Here's a rundown of the best features of each of the four programs, along with some useful tips on how to earn more points and redeem them smartly. We've also provided a detailed, side-by-side comparison of each program in two tables, one on earning points and the other on redeeming them.

Ultimately, deciding which card is right for you will depend on how you plan to use the card and what you'd like to do with your points.

American Express Membership Rewards
What we like: Membership Rewards is the oldest such program, and it still holds the lead in terms of the range of rewards offered. It boasts a strong travel section and is the only rewards program that allows you to combine your points with one of 15 frequent-flyer programs.

Our favorite feature is the ability to earn points by taking advantage of the many promotions (usually short-lived) that AmEx runs for using services provided by specific partners. (That's provided, of course, that you were already planning on using these services.) Currently, you can earn 1,300 bonus points on each $10,000 of a mortgage you finance through Citibank, Chase, Washington Mutual, or Wachovia, if you go through the AmEx web site. You can also get 2,000 bonus points for each wireless service line you open with SprintPCS, up to 10,000 points.

What we don't like: Slow earn rate otherwise. You earn only a point per dollar spent, unless you carry the pricey AmEx Green or Gold Preferred Rewards cards ($110 and $130 annual fees, respectively).

Citibank ThankYou Network
What we like: Citibank has a clear advantage in the everyday earning category: depending on the credit card you get, you can earn two, three or even five points per dollar on specific purchases. With the Citi PremierPass card, you even earn points for the miles you fly.

We also love the ability to accelerate your earning power through Citibank's ThankYou Merchants network. All you need to do is register your Citi card and use the ThankYou Merchants web site as a shopping portal. If you need to buy something from Overstock.com, for example, go through the ThankYou web site, click on Overstock in the "Shop & Earn" section and it will take you to the original Overstock.com. The difference: Now you'll earn seven bonus points for each dollar you spend, in addition to the point-for-dollar earnings when you use your Citi card.

What we don't like: Most credit cards cap the amount of points you can earn each year. The Citi Diamond Preferred Rewards card for example, limits you to 75,000 points during any calendar year. (The caps vary depending on the type of card you have.)

MBNA WorldPoints
What we like: Redemption choices abound. You can redeem points for cash, merchandise, travel and gift certificates, including Visa- and MasterCard-brand gift certificates that you can use anywhere and for anything you like. (It's smarter than redeeming for cash, which will cost you 200 points per dollar, vs. 130 points with gift certificates.)

What we don't like: Points expire after five years. There are no promotions and only three bonus point opportunities (see table). Point-per-dollar redemption rates are higher than those offered by Citibank and American Express.

Visa Extras
What we like: The Visa Extras program has the most generous bonus point program you can earn up to 20 bonus points on each dollar spent with certain merchants (see table). It works like Citibank's ThankYou Merchants program: You have to go shop online by going through the Visa Extras web site first.

What we don't like: You need 20,000 points for a $50 gift certificate. In addition to that, you typically earn just one point for each $2 spent on regular merchandise.