My advice is get Sirius! It will soon be standard on the new 5's It's much better than XM.
Sirius sounds the best, has the most varied programming, including the NFL, and they soon will have streaming stock quotes and sports scores. Sirius has 3 geosynchronus satellites at a high elevation orbit that provide superior line-of-sight coverage. Here's a link to the Sirius website explaining the differences: http://www.sirius.com/servlet/Conten...=1065475754125
And here's a graphic showing the satellites and orbits of both the Sirius and XM satellites. http://www.tiger-usa.com/sirius-xmorbitanim.gif
If you are near a Sound Advice, check them out. My local Sound Advice specializes in BMW's and Mercedes installations.