Satellite Radio Questions

[HDPM]

With the exception of my decent home stereo speakers, I am pretty much at the bottom of audio or other electronic entertainment stuff. So I went to a couple of stores looking for car audio today. The stock AM/FM/casette in my rig isn't so hot. So I looked at new decks w/ CD and speakers. I also looked at the new satellite radio stuff. One store deals with XM radio, another with Sirius. I think the whole idea of satellite radio is cool. Where I live and drive the radio selections are limited. I like the idea of getting jazz or hardcore rap or classical in the middle of nowhere. Anyway, anybody have this stuff in their car or know something about it? Is one service better than another etc...?