Apple's App Store remains the mobile-app marketplace king with the largest number of titles, but Android Market saw the highest growth last year, surging by more than 500 percent, according to a report released yesterday by Distimo.

Tracking the growth of the major mobile-app stores for the U.S., the 2010 Distimo Report found that the Apple App Store grew the most in terms of sheer numbers, doubling its selection of titles to almost 300,000. In second place, the Android Market currently offers fewer than 130,000 apps. But Android apps enjoyed the biggest percentage gain for the year, growing by 544 percent.

The BlackBerry App World also showed nice gains in the number of apps, rising by 268 percent to reach almost 18,000 apps, while Nokia's Ovi Store grew by 258 percent to offer around 25,000 titles, according to Distimo.

Free apps were more prevalent than paid ones, the by-product of developers seeking ways to make money beyond charging for their programs. Each of the four top app stores saw higher growth in free apps alone than for their entire stock. As one example, the number of free titles in Nokia's Ovi Store jumped by 899 percent for the year.

Which apps were among the most widespread in 2010 Distimo's findings revealed a couple of surprises.

Though the iPhone has traditionally been targeted toward the average smartphone consumer, business-oriented apps were prominent in Apple's App Store, a sign that more people are adopting the device as a productivity tool, according to Distimo.

On the flip side, Research In Motion's BlackBerry has been considered more of an enterprise tool, but BlackBerry App World trended toward e-books, music, and other entertainment titles. Google's Android Market and Nokia's Ovi Store tended to show a more balanced range of product categories.

Looking at specific apps, Facebook, Skype, Google, and Twitter were among the 10 most popular free apps in Apple's iPhone App Store in terms of downloads. Excluding games, Google Maps, Facebook, Gmail, and Twitter were top free titles at Android Market. And BlackBerry Messenger, Pandora, and Facebook were in the top 10 rankings at BlackBerry App World.

Based in the Netherlands, Distimo provides analytics for mobile-app stores.