Xm has more subscribers more channels, less cost per month ($10) and now is commercial free, they are also putting up 2 more satellites for a total of 4 next year via Sealaunch---
XM has a pretty good fansite here
http://www.xmfan.com/ where you can discuss the pros and cons thru a messageboard and look up equipment deals, satellite stocks, suggest songs etc
At
http://www.xmradio.com/ you can listen to live music feeds, see how it works, see who manufacturers equipment for home/car/boombox/PC (XM PCR for computer use is less then $50 for the equip) and personal use (you can ride a skateboard/bicycle etc and listen to XM on a walkman type unit) I get a weekly email from them telling me about the weeks special programming, live concerts, and current sat radio events...
I have XM in my car and house (they offer family plan deals for multiple units, additional subscriptions are $6) and I also have the boombox, and ported the signal to my PC from my home unit so I can record satellite programming to it...
I think no matter which way you choose you will be happy to break away from commercial radio...
(Edit---> XM PCR is under $50
http://www.xmradio.com/xmpcr/)