Technology
Again, Sirius takes the category as they have three satellites at high-elevation geosynchronus orbit while XM Radio has two geostationary satellites at low-level which would allow more obstruction. From what I can see though, both Sirius and XM receive good signals and seem to work nicely.

So why pick Sirius? Because they use statistical multiplexing which allow channels that need more bandwidth to use it giving the user clearer highs and deeper bass.

Well, to put it simply, fantastic. Depending upon the receiver one chooses, you will notice clear highs, deep, resounding bass, and a clear mid-channel. To put it in terms we would understand, I'd say the audio sounds at least as good as a 128kb/s MP3, but is not quite CD quality.

But what if you're under a bridge, or in a downtown area? Unfortunately, you've come across the weakness of satellite radio. The L-Band transmission can penetrate some objects (including my wooden house), but bridges and buildings block the transmission. Fortunately, both XM and Sirius are going to install some 1,000 repeaters throughout the country. These repeaters will also broadcast on the L-Band frequency. The antenna will pick up this signal as well, and as noted above, the signal will go down the Terrestrial line into the receiver, for supposed un-interrupted reception. They face some fierce opposition though, from Mobile Phone companies, and traditional broadcasters represented by the NAB.

However, at times the service has been dismal. And there is nothing to point to as the cause. It can be a bright, clear day out, and at around 5 pm, on my commute home, service will simply be awful as I drive through a mountain pass, whereas just the day before, service was un-interrupted. I'd say this happens around 5% of the time, but it is enough for me to mention it. The other 95% of the time, when I'm driving in the clear, there is no problem at all with reception.