2013 has been a strong year for Sirius XM Radio ( SIRI) -- the satellite radio company has seen its shares rally more than 30% since the calendar flipped over to January, more than doubling the S&P's ascent year-to-date. Sirius XM provides subscription-based radio coverage to more than 25 million subscribers in the U.S. and Canada. Beyond satellite, Sirius has made big investments in its online platform of late, adding options like on demand programming to the mix. >>3 Hot Stocks to Trade (or Not) The breakneck growth of auto sales in 2013 is trickling down to SIRI's income statement. With satellite radio transmitters installed in more than two-thirds of new cars sold today, the firm has a captive audience that's excited to play with the features of their latest big purchases, including free trials to SIRI's services. As a result, the firm converts close to half of those trial users into paying subscribers. Size matters in the content business, and Sirius XM's scale means that the firm can afford to pay for exclusive names and pricey content partnerships for sports and music. Even though rivals like Pandora ( P) are competing to grab consumers' drive-time attention (and dollars), SIRI's dominant integration and superior service coverage gives it a major advantage in the shootout.