I'dd reply too, just because this question comes up often enough if someone seacrhes first it should answer a few questions.
If you want the factory sat, then you'll have to go sirius. If you are doing an FM mod or have/will buy an aftermarket sat radio, go XM. They have a greater variety of music and the talk channels aren't too bad either. Sirius does have more talk though. The SQ on each should be the same.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>