I have the Sirius right now, used it once.
I highly, and i mean HIGHLY recommend Google Play Music instead through Bluetooth from your smartphone.
It's $10/mo, unless you only want to use the upload/playback feature (See #3 below) - that feature is absolutely free.
Here are some cool things it can do:
1. Find almost any song and artist, including TONS of international music!
2. Just like Pandora, you can start a radio from every song. Unlike Pandora, it doesn't repeat songs after 20 tracks.
3. Google lets you upload up to 50,000 of your own songs from your desktop computer that you can listen to or download to another device anytime (up to 300meg/song)
4. They give you suggestions on what you may like - and this feature works quite well!
5. You can always click on a song, go to "View Album" and see what other songs are there and even play entire albums, or you can see related artists, and related songs. This is very addictive... i end up doing this for a long time then realize i just wasted 2 hours staring at my phone...
6. Has unlimited skips, and you can scroll down to see what tracks are coming up 
7. You can SAVE your radio stations and playlists and playback from any other device.
8. Track info gets displayed on the car's display.
And much much more...
And before you ask, no, i don't work for Google, i just really like Google Play Music.
Forgot to add: It streams in high quality at 320KBPS+ if you select that option. It's off by default due to usage plans on cell phones, but if you have a lot of data, turn this feature on.
