XM or Sirius

I want satellite radio, but which sounds better? The more I read, the more it seems 50/50, yet some are so convinced. I wish Sirius had an analog digital out unit like the Polk, so I can run the signal through a dac. And I do like the idea of $500 lifetime with Sirius. Please advise.
I bought Sirius at the end of last year before Howard Stern jumped to satellite. From personal experience and what I've read I agree with what Mikelavigne has said. The sound quality is poor and the signal is finicky. I hear equal complaints from both sides. I can even sometimes hear a "tinny-ness" to the sound through my headphones. The decision really comes down to programming, the features of the unit for your application and subscription packages.
Mikes experience mirrors mine, I chose Sirius for content and I do like the lifetime membership.
In two of my cars, one has XM and the other Sirius integrated into the sound systems. To me the audio quality seem the same. I much prefer the Sirius programming (jazz, sport, rock) although the XM programming also pretty good. My son put an after-market add-on XM unit in his car and the sound quality was not good with spotty coverage. In my experience, it seems that the add-on units are not as good as the integrated units.

Good luck,

Same as what's already been said. I have Sirius in my car, but have had a large number of rental cars which typically give you XM. IMO XM has better jazz and blues stations, with deeper playlists than Sirius. XM also has deeper punk and alt playlists (again IMO). Sirius may have the edge on pure Rock 'n' Roll. Classical is a toss up so far. They both sound like cr@p compared to a high end system and source (I sometimes bring my radio into the house and hook it into my system).
Actually I am quite pleased with the sound quality of XM service using a Polk tuner through a Benchmark DAC. Granted it is not nor do I think ever could be "CD quality" as claimed, but some formats (Jazz, Classical, Instrumental) sound pretty close. Format wise I think both are about the same from a music standpoint, X the differences like Stern or XM's version of anoying talk show hosts. I chose XM for home use due to the inclusion in my GM vehicle as I already had an account, and the fact that Polk was comming out with a home tuner with analog output to a DAC. Not sure if anyone has a similar tuner available for Sirius but I am sure if not they will soon.