iTunes may be cool. It has the brand name. It leads the market for online digital music sales by a large margin. But AmazonMP3 has something iTunes does not: all four major record labels selling music free of copy protection, or digital rights management.

Sony BMG, the world’s second-largest record label, will start selling DRM-free music on AmazonMP3 at the end of the month, confirming reports that surfaced last week. And, best of all, fans of Sony BMG artists like Britney Spears and Bruce Springsteen will not have to drive to brick-and-mortar stores like Best Buy and Target to purchase Platinum MusicPass cards just to download music free of copy protection.

With Sony BMG now joining the other big labels, EMI, Universal Music Group, and Warner, AmazonMP3 has a clear advantage over iTunes for consumers who want the songs they purchase to be playable on virtually any computer and portable music device.