I used to be a staunch advocate of XM, then they got rid of XM Liquid Metal. Why did they get rid of their second most popular rock station? Well, they got a license with MLB and thought it was necessary to set up 3 stations for it. I think it's something like this: the first is live baseball coverage, the second is repeats of prior games, and the third is "Major Leage Baseball en Espanol". The funny thing is that their Christian stations (all three of them) have some of the lowest ratings in their lineup, but getting rid of them would cause a stir. So they decided to axe the new black/death metal station.
I'm seriously looking into Sirius at the moment. Squizz, the only "hard" new rock station they have has gone to pot in a flood of pop-rock. Atleast they play Rammstein, Cradle of Filth, Ministry, Mudvayne and Marilyn Manson to make up for it. Plus, XM just anounced a rate increase from $9.95 to $12.95, so I'm not so happy about that either. It's sad that I listen to more CDs than subscription radio because of this.
But as far as reception and audio quality goes, XM is great. I've never had a problem with reception unless I was in a parking garage or something and the signal was blocked. The audio quality is about the same with both. There may be subtle differences, but it doesn't make one any better than the other.
EDIT: Both Sirius and XM have a free 3-day online trial period. The quality isn't good, but I'm listening to Sirius right now
