I may be biased when it comes to satellite radio, since I subscribe to both Sirius (NASDAQ:SIRI) andXM Satellite Radio (NASDAQ:XMSR). I am also a fan of both companies, so much so that I've singled out shares of XM to Motley Fool Rule Breakers subscribers.

Sirius and XM have had good runs thus far. They were seven-baggers before peaking in the fall of 2004. The shares haven't fared that well since, though both companies continue to line up new subscribers at a fantastic pace.

That brings us to this week's bout. When it comes to Sirius, not all Fools agree. This week, Tim Beyers argues in favor of Sirius, as Alyce Lomax counters with the bearish argument. Is satellite radio for real? Are terrestrial players like Clear Channel (NYSE:CCU) and Cumulus (NASDAQ:CMLS) quivering with fear? Can millions of subscribers -- and counting -- be wrong?

Does Sirius belong in your portfolio? That's what this week's Duel is all about.

Duel on!