Sirius XM Radio (NASDAQ:SIRI) hit a fresh five-year high today.

That isn't really much of a surprise. Sirius XM pleased investors earlier this week by announcing that it wrapped up the second quarter with 715,000 net new subscribers. There are now more than 25 million subscribers for the satellite radio service.

Sirius completed its merger with XM in the summer of 2008, making this the highest price since the formation of the satellite radio monopoly.

The stock's ascent to its highest market cap -- ever -- comes during the same week that finds streaming radio bellwether Pandora (NYSE:P) taking a hit after posting a surprisingly large sequential monthly decline in listener hours and radio market share.

Despite the urge for investors to pit Sirius XM against Pandora, both companies have been able to grow in recent years. Pandora may be growing faster, but Sirius XM is the consistently profitable one with a huge base of paying customers.

Are we at a point where the two non-terrestrial radio bellwethers are diverging?

Sirius XM should continue to prosper. Auto sales remain strong, and every year finds older cars without satellite receivers replaced by vehicles that have Sirius or XM players. The improving employment scene means more commuters on the road, and the buoyant economy makes it easier to stick to the monthly pricing plans.

Pandora would seem to be a beneficiary of the same trends, especially now that it has deals in place with most automakers to stream the popular app through car speakers for drivers with Bluetooth connectivity. However, Wall Street pressure to monetize freeloaders at a time when tech giants are slapping on their swim trunks to dive into this pool, offer more uncertainties for Pandora investors in the near future than Sirius XM shareholders face.

Sirius XM has become the face of premium radio, and now, it's taking over the ears.

Longtime Fool contributor Rick Munarriz has no position in any stocks mentioned. The Motley Fool recommends Pandora Media. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.