My car came with Sirrus, HD Radio, and the iPod adapter. I have listened to all 3 but my preference order is iPod, HD Radio, and then Sirrus. I have even thrown a CD in the car just to make sure it worked.

There are several downsides to Sirrus compared to HD.
1. I get occasionally intermittent reception (bad weather, in cities surrounded by buildings, etc). HD radio is local strong stations.
2. The sound quality isn't that great. HD seems better.
3. Even with no "commercials", there seems to be a lot of interruptions between songs. Only a slight win over HD.
4. If I listen to the radio, I like local weather and traffic info. I can't get that on Sirrus for Charlotte.
5. After 1 year, you pay for Sirrus, HD is free.

The plus sides to Sirrus
1. Great selection. Doesn't matter to me since I like the Rock & Roll played by local stations. I wouldn't want to listen to 3 straight hours of 80s music anyways.
2. No need to switch channels if you travel. I don't travel but have the iPod to listen to if I did. If I wanted to, I wouldn't repeat a song on my iPod for almost 5 non-stop days (115 hours of music).
3. The NFL on Sirrus. I'm not a BIG NFL fan but when I did try to listen to the Panthers while out of town, they weren't on Sirrus, I could only find about 1/2 the games.

I let the Sirrus subscription in my '06 650i lapse. I'll likely do the same with the 550i.

 

I did that once in my 2006. It jammed, had to go to the dealer, and they had to replace the CCC.