I think Sirius has better sports too with exclusive deals with NFL,NBA,NHL, College Sports Network
It does have better sports - the NFL deal was huge. I am more of a baseball fan, though, and MLB signed with XM. I like the idea of every baseball game available on radio for me (or most every game).
Honestly when both Sirius and XM come out with neat handhelds (XM already announced theirs) I'd consider saving up and getting both. The trick is that the handhelds don't require setting up antennas in your car and home (antenna is built in), and the unit comes with both home and car docking stations.
So I'll drive with Sirius and keep my XM in the glove compartment - I'll listen to baseball in the spring/summer when a good game in on, and Sirius the rest of the year.
Neat, small docking stations for home make home ejoyment of each easy.
It's good stuff.