I started with XM 3 years ago and added Sirius also so I can speak to both. In fact I have both the XM Traffic and sirus recievers hooked up to my Z1. The difference in sound quality, less commercials, better signal strength, less cut outs, all go to Sirius. I never listen to music on XM, the bandwith on their channels SUCKS... I like both for Sports, traffic etc, but if I had to choose one it would be Sirius. It is widely known that XM has bandwith issues on many channels, thats why their talk channels sound like you are listening through a tin can an string.
