My conclusion is that there are cheaper and better alternatives to satellite - but you have to be prepared to invest in some hardware to get a system that is as convenient as Sirius.
What I have now:Pioneer receiver and older XM radio unit that can store satellite radio for offline play. The music from the XM radio unit is then sent via FM signal to the Pioneer in dash receiver.
The good: In the mountains I switch to the stored radio programming and can still listen to music. With a push of a button I can switch to different stations.
The bad: I'm getting tired of the Sirius Dj's and am finding the music kind of stale. I'm also tired of paying for radio when so many internet stations can be listened to for free from a desktop computer.
What I've migrated to:
Step 1 in making the switch away from satellite radio was to upgrade my in dash stereo to one that supported bluetooth. This was key - as it allowed me to easily connect my iPhone to the receiver with no wires (or without even having to take the iPhone out of my pocket). I've tried wired connections to my existing stereo and found that this added one other level of complexity that I didn't have with the satellite receiver. As soon as I installed my bluetooth compatible receiver and paired with my with iPhone i was able to start streaming any audio from my iPhone to car stereo really easily - and control the playback using the stereo (pause, skip, etc.).
Step 2 was figuring out how/which service to use on my iPhone to replace SiriusXM radio. I spent a lot of time researching this and ended up using a combination of three apps on my iPhone. For me the two driving factors were cost and offline playback. I live in Vermont and we have pretty poor cell coverage - so for the majority of my commute I have no signal and have to rely on offline playback mode. I ended up with three apps all of which support offline playback.
Google Music + Melodies (app).
The melodies app allows me to store playlists on my phone directly from my google music account. My google music account has 3,000+ songs - so I just create a few playlists that have genre/artist mixes and then store them for offline play. This way I can play favorite songs easily no matter where I am and update the playlists to keep the combinations fresh. This doesn't expose me to new artists and tracks so my next addition was
Slacker Radio iPhone app
You have to pay $4.99/month for offline playback - but when you do the slacker iPhone app rules. You can store a few stations (each of which will load around 1,000 songs) to you have this massive collection of offline music for playback. Switching from station to station was pretty easy on the iPhone and the bluetooth connection streams not only the music but the artist and album as well. The only downside was the $$ for the monthly subscription - but it was still much cheaper that Sirius. You also have to allow a loooong time for station downloading (several hours) and also have a few gigs free space on your iPhone to store the station songs.