Sirius or XM better quality?

I have a Sportster Replay and the quality of the music is horrible. I listen over the FM broadcast but have also tried wired connection. The quality is much worse than any FM staion. I listened to a built in unit in a friends car and it sounded better so maybe it's just a poor receiver. I wonder if anyone has tried both and could comment on differences. I'm in Los Angeles in case you could comment on reception differences. This is to install in my new 2010 (so it's relevant).