NEW YORK (CNN/Money) - The 2004 models are starting to roll into dealer showrooms, and to make room, dealers need to get rid of last year's models.

What should you do? Be the first kid on the block with a brand-spanking new model, or go for the savings on 2003 cars?

There are two key questions you first need to answer:

First, is there a big difference between the 2003 and 2004 versions?

Second, how long do you plan on keeping the car?

If the answer to the first question is "No," you don't need to think much about the second question.

You can save yourself a lot of money by snapping up a 2003 model. If you don't hurry, though, you may have to sacrifice getting the color and options you want.

These rules apply only if you're buying the car, though, said Joe Cashen, director of pricing for Carsdirect.com. If you're leasing, the higher residual value of the 2004 model will mean lower lease payments.

But if the car you want has been substantially redesigned for 2004, the amount of time you plan to keep it could make a big financial difference.

Most car models get a radical design make-over roughly every four or five years. (The accompanying table lists the major ones for the coming model year.)

So in four years, your just-redesigned 2004 car will look much newer -- and be worth much more -- than a 2003 model.

In fact, the 2004 could be worth $3,000 to $4,000 more at trade-in time, said Paul Calisi, president of AAA New York's auto buying program.

That extra $3,000 to $4,000 may very well completely offset the savings you'd get by buying last year's model. "And you're driving what might be a technologically superior car," said Calisi.

If you'll be keeping the car for more than five years, a 2004 redesign won't add much value by the time you're ready to sell the car or trade it in. By then, another design generation will have passed.

In that case, think about how much you're likely to save by buying the older version and decide if any improvements in the redesigned version, including the new look, are worth the price.

If you decide you really must have the 2004 version, you might want to wait a while. If the car was heavily incentivized before, chances are it will be again. Those incentives might start showing up around October. (For more on 2004 incentives, click here.)

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Compare features on the 2003 cars to see what, besides a new design, the 2004 brings with it. For example, the newer car might have a different engine, side air bags, more interior room or other amenities you won't get with the older version.

When comparing the cost of the 2003 and 2004 versions, watch for items that were standard equipment on 2003 cars that become options in 2004, said Cashen.

That's one way that carmakers can make car prices seem to stay flat year over year. Some car Web sites, including Carsdirect.com, have tools you can use to compare features and prices between one model year and another.