So many iPhones, but which one is right for you?

Apple (AAPL) has sold a lot of iPhones since introducing the novel smartphone to the U.S. market in 2007. But after eight generations and about 900 million sold, could it be that demand is finally flaming out? Apple's latest earnings report certainly has people talking that way.

Despite concerns about slowing demand, the iPhone remains as popular as ever. According to a Reuters/Ipsos poll, 86 percent of iPhone owners were somewhat or very likely to buy another one. Of those likely to buy a phone, 15 percent are currently looking to upgrade, and 17 percent will do so when the next iPhone is released, according to the January poll.

If you're weighing an upgrade, you may be wondering which iPhone to choose or whether to wait for the iPhone 7, rumored to debut in September.

It's, as they say, complicated.

Currently, Apple sells four iPhone models: the iPhone 5s (introduced in 2013); the iPhone 6 and larger 6 Plus (2014); and the 6s and 6s Plus, which went on sale last fall. The newest models, of course, offer the latest features (and cost the most), but you may not need all the bells and whistles that come with the latest models.

So, comparing features may help you save money. For example, the cheapest version of the recently introduced iPhone 6s costs $649. Compared to the older iPhone 5s, which despite being out for more than two years remains competitive, the 6s has a more powerful processor, a better camera lens and 3D Touch, which senses the amount of pressure applied to the display. But if you can live without those features, you'll save $199.

Adding to consumer confusion is speculation that Apple will soon roll out an updated version of the iPhone 5s -- the iPhone 5se -- that would sell for less than the top-of-the-line 6s model. The 5se, which includes many updates over the 5s, reportedly is aimed at the millions of 5s users who haven't upgraded to newer models, in part because they like the smaller size of the 5s.

According to the rumors, the 5se will keep the same 4-inch screen of the 5s and maintain other similarities that would possibly allow 5s users, for example, to keep their current protective case. That would remove one impediment to getting consumers to upgrade -- the cost of new accessories, which can easily boost the price of new phone by $40, $50 or much more.

Also weighing on consumers' minds are any changes Apple may be planning that could alter the way users charge or connect to other devices. Many iPhone fans expressed outrage after Apple switched to its new "Lightning" dock connector in 2012 with the iPhone 5. The new connector replaced a 30-pin connector that had been used for nine years. The new, much smaller plug allowed Apple to build thinner iPhones and was easier to use, Apple explained.

But some consumers saw it as a conspiracy, suggesting Apple made the switch to boost sales of pricey adapters that consumers would need to use older accessories. Fortunately for iPhone fans who may be considering upgrading soon, there's no indication that Apple plans any similar change.

Of course, it's the hefty cost of the phone itself that has many consumers weighing whether to upgrade. That wasn't always case. Until recently, all the major carriers subsidized the cost of a new phone as long as you were willing to sign -- in most cases -- a two-year contract. For iPhone buyers, that meant you could get the latest iPhone for as little as $199 (plus taxes and fees).

But Verizon (VZ), Sprint (S) and others have abandoned the subsidized-phone model, leaving iPhone fans to foot the full bill should they choose to upgrade (though monthly payment plans are available). AT&T (T) remains the only major carrier with a subsidy program.

Whether to upgrade your iPhone ultimately is a personal choice that's often driven by other than pragmatic considerations -- not unlike buying a new car. Chances are, however, if you own an iPhone 5s or 6, you can probably wait to upgrade. Then again, if you're a follower of fashion, don't overlook that new "rose gold" color iPhone. Wouldn't that just look sweet on your nightstand?