NEW YORK (CNN/Money) - No money down, no interest, hefty rebates: automakers have been tantalizing us with deals like these for a year now, keeping auto sales speeding along even in the face of a slow-lane economy.

Now, with the model-year changeover adding more incentive for dealerships and carmakers to move inventory off their lots, car-buying has never been more enticing. But which deals should you take and, with 2002s sharing dealer lots with 2003s, which cars should you buy?

Those incentives have been good for the car companies, at least in the short term, as well as for their customers. Both Ford and GM reported earnings this week, boasting numbers for the third quarter that beat Wall Street's expectations.

But September sales tapered off a bit from August. Early that month GM withdrew some 0 percent financing deals on '02 models, and their sales dropped in response, said Dan Hubbert, a GM spokesperson.

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The September sales dip taught automakers their lesson. Take incentives away and customers will hold back, too. GM is now offering what they are calling the "zero, zero, zero" incentive package -- no down payment, no interest, and no payments for 3 months on new 2002 and 2003 cars.

Whether sales can keep going in the fourth quarter of this year, as more and more potential new car buyers become new car owners -- and with customers who expect another great incentive package at every corner -- remains to be seen.

Auto sales experts differ on whether sales will flag significantly in the next quarter. Ashley Knapp, a researcher at AutoAdvisor.com, predicts sales will drop this fall and winter, as American consumers get 'tapped out'. John Honiotes, vice president of automotive operations at Autobytel.com, says plenty of people still need cars, and baby boomers in their peak buying years will keep on buying.

But all the experts agree on one thing: incentives like the ones we're seeing now will be here for a while.

Keep in mind, though, that rebates and incentives aren't available on every car, because they're simply not needed on every car. Incentives are targeted to sell cars that are in oversupply.

"2002 models are running out," said Honiotes. "That's a nice problem to have. And people forget there are no incentives on hot products. There are no incentives on the Nissan 350Z. They don't need to sell a million Ford Thunderbirds, or Honda Odysseys. But there's a reason -- incentives are there to keep the plants open and for automakers to keep moving products."

So, what's a savvy customer to do? Tough decisions abound. Buy now or wait for even better incentives? And with all those 2002 cars still on the lot, does it pay to take the "older" model?

The good news is that since incentives look like they're sticking around, you may be able to get a good deal on a car even if you wait a while. (That's unless you're hoping to buy a 2002 model. Then you have a different problem: time may run out unless you act fast, because 2002 inventory is so low.)

"You can't get a better deal than zero zero, unless automakers start making payments for you," said Honiotes. "But things will stay as good as they are now, at least for the next year."

If you want a 2002 model vehicle, buy now. A cost-conscious shopper who wants to get the best possible deal and plans to stay in the car for more than 4 or 5 years should probably opt for a 2002 model, said Honiotes.

While deals are good on some 2003 models, they're even better on 2002 models that dealers are trying hard to clear off their lots. For example, while you can get up to $2,500 cash on a 2003 Ford, you can walk away with as much as $4,000 on a 2002 model.

On the other hand, if you're positive you'll be getting rid of the car in a couple of years, you don't want a 2002, Honiotes said. The reason is trade-in value. With an older model, more value is taken away for depreciation at trade-in time. Over a short time frame, that one year makes a big difference.

If you're looking at something that's only available in a 2003 model, like the Nissan 350Z, it will pay you to wait a while, Honiotes cautioned.

"If you have the first one on the block, you'll pay extra money for it," he said.

While zero financing may sound and may indeed be great, there are a few things to keep in mind.

First, in order to take advantage of a zero-percent financing deal, you have to qualify for it, which means you need a tip-top credit report.

Also, remember that the terms on zero-percent financing loans can be short, which means fewer, bigger payments. For the most part, zero percent financing on Ford cars and trucks is only available on 36-month contracts. If you can't afford to have those big chunks taken out of your bank account each month, zero percent isn't really doing you much good.

Picking through the current cornucopia of catchy financing deals can be daunting. More options are always better, but you have to be sure you know what you're doing.

"You need to be more sophisticated these days in comparing factory cash back to leasing alternatives to financing," said Bob Brisco, CEO of CarsDirect.com. "It takes more time, and more math. I think that's a real issue for a lot of people -- lining up the best deal for you can be tricky."