Sirius XM Radio (NASDAQ:SIRI) had a healthy run atop the music category in Apple's (NASDAQ:AAPL) App Store, but it's Pandora's turn now.

Pandora's music-discovery application is once again the top draw for iPhone and iPod touch radio buffs, where it has typically reigned since last summer's App Store launch. It was bound to happen. Sirius XM was putting plenty of marketing muscle behind its web-streaming application, but Apple users have a funny way of gravitating toward free content. I guess after paying $20 or $30 a month for unlimited data, slapping on another premium is a hard sell.

Sirius XM Radio fans will argue that their product is superior, though Pandora certainly has its charms. It spits out customized playlists based on your preferences, getting better as it collects more data. It's a model that works well for Netflix (NASDAQ:NFLX), (NASDAQ:AMZN), and TiVo (NASDAQ:TIVO). It also helps that you can skip through a song you don't like, something that satellite radio can't do within the same genre-specific channel.

Pandora's weakness as a true proxy for Sirius or XM is that it's just about music. There's no news. There's no Howard Stern. Unfortunately for Sirius XM, there are other free streaming apps including Stitcher, Yahoo!'s (NASDAQ:YHOO) Y! Music, and a public radio tuner that help fill the talk radio voids. And that's the beauty of free apps. You don't have to download just one.

Sirius XM did make the most of its time at the top, amassing more than a million downloads over a couple of weeks. The company has not gone public with the number of actual activations of the premium service, which is what will ultimately dictate the app's success.

Losing the yellow jersey isn't the end, of course. The downloads will continue, though at a slower pace unless a free ad-supported version is launched.

App Store shoppers are simply showing their true colors again, flocking to either free apps or those that involve a single upfront payment.

What would you do to get the Sirius XM app back on top of the music heap if you were CEO Mel Karmazin? Post your thoughts below.

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