I had XM for 4 years and just switched to Sirius. We originally got it for the boat and liked it so much we put it in all our cars. I think Sirius has a better selection for music and XM for talk and sports. If you are a Howard Stern fan Sirius has 2 channels 24/7 for him.
Check out
www.sirius.com, you can get a 3 day trial to listen online, which has pretty good quality.
