I have XM actually…the big reason for me was because it had MLB. I wish the same brand got both MLB and NFL, then I would be really happy. 🙂 XM will be losing Nascar to Sirrus after next year I belive. You can catch an NBA game every so often on XM if ESPN radio is broadcasting a game, however, Sirrus has the full package.
Opie and Andy is actually free now. I tried listening to it a bit when I was down visiting Jarrod and Elliot over Memorial day, and they wore on me very quickly.
Music wise, from what I understand talking with Duncan, it’s fairly similiar. Although, XM does have a movie score channel if you’re into that sort of thing. Also, one other channel that I tend to stick on XM a lot is called ‘Fine Tunning’ which crosses a lot of genres to get, as they term it, ‘The World’s Most Interesting Music’
I have the Delphi MiFi, which is a handheld portiable radio. I do understand that Sirrus will be coming out with their own version of this in the next few months.

Well, I’ll temper my comments by saying I don’t have a lot of experience with XM. Sirius has two NPR channels plus PRI, although it’s worth noting that these are basically replays of their most popular shows like The Connection, Day To Day, etc. They don’t have and probably will never have Morning Edition or All Things Considered. XM has one “public radio” channel that they’re building around Bob Edwards’ show that pulls from Chicago Public Radio and WGBH Boston. Otherwise the two networks news/talk lineups are similar, though XM will (eventually) have Air America exclusively, and Sirius has a pretty good gay/lesbian talk station, OutQ.
Musicwise the two networks are similar, though each plays to different specific interests. If that’s important to you I’d suggest comparing the lineups on their websites. Neither has a Celtic channel, which really chaps my hide. That would be a nice thing to get. On Sirius, at least, Celtic stuff pops up on teh Horizons world music channel and Folktown.
Sports is where the two Networks really differentiate themselves. Sirius will have all of the NFL and NBA games as well as a good chunk of college football and basketball games, plus English soccer play by play and the NHL, assuming they ever get their act together. XM has all of the MLB baseball games, PGA golf (!?), and Nascar and IndyCar racing.
Oh, and if you care about shock jocks, XM will have Opie and Andy (for an extra fee), and Sirius will have Howard Stern eventually.
So there you have it. As far as hardware goes, it seems like the offerings for the two networks are basically similar. If you go with Sirius, I highly recommend the Audiovox PNP3 unit – good ergonomics, simple to use, and pretty reliable so far.