• by Mark Walsh  @markfwal, April 27, 2011

iPhone and Android device owners are the most active smartphone users when it comes to apps, according to new data released by Nielsen today in connection with the AppNation conference in San Francisco.

iPhone and Android owners make up the majority of U.S. smartphone users and nearly three-quarters (74%) of app downloaders. Furthermore, iPhone and Android users have more apps on their handsets than people with other smartphones, with an average of 48 and 35, respectively. The average is 15 for BlackBerry owners.

iPhone and Android users also engage with apps more often. Some 68% of iPhone app users and 60% of Android app downloaders reported using programs multiple times a day, compared to 45% of BlackBerry owners.

In addition to their smartphone share, Apple and Google enjoy an advantage over rivals in the size of their app stores. The App Store boasts more than 350,000 titles (and 10 billion downloads), while the Android offers some 225,000. The app storefronts of BlackBerry-maker Research in Motion and other smartphone competitors do not yet approach those levels.

On Tuesday, Nielsen released new findings showing Android had edged ahead of the iPhone as the preferred device among in-market smartphone buyers: 31% to 30%. And half of those who had bought a smartphone in the past six months said they had chosen an Android device.

Nielsen also said more than one-third (36%) of U.S. mobile users now have smartphones, up from 31% at the end of 2010. The research firm has previously predicted smartphone penetration will pass 50% in the U.S. by the end of 2011.