I had a free trial for a month on one of them. I thought they had a better selection of music. It was a little cumbersome linking my phone to my car radio, and where I live, there were some areas of dead air. Sirius was cheaper, especially when you went through the misery of trying to drop the service and they would offer you 6 months at $5 a month, but I just stick with FM. I'm not that avid about having the radio on when I'm driving.
I also have an aversion to monthly subscriptions where my bank account is in the hands of some service provider.