I gotta give the vote to XM.
My rationale....XM now has the SKIFI2 reciever. It can be used in your car or home via either the FM modulator (tune to a radio freq and voila!) or you can use the tape adapter.
The SKIFI2 also allows you to pause the live radio, rewind it, and replay it over and over...for those of you that like to listen to things over and over.
The unit also allows you to save your favorite songs or artists. What happens is if lets say you choose AC/DC....you hit the button then whenever AC/DC is playing on ANY station there will be a small beep from the reciever and it will show you what channel and what song it playing. If you would like to listen just hit the XM button and it tunes you to that channel! VERY COOL FEATURE THAT I LOVE!!!!!!
You can also get stock quotes, sports scores, etc on the scrolling display.
I have friends that have both and the ones that have the sirius models (and older XM Skifi) wish they had the SKIFI2.
My 2 cents but XM very worth it in my book.
Regards