We (my wife and I) have XM. I have an Alpine unit hooked up via an FM modulator, and my wife has a roady with wireless FM modulator. Hooked up directly you will get better sound quality, then you will via the wireless modular. If you have a radio that will accept an XM module direct, that will be the absolute best quality. But I love the roady unit. I want to put one in my car. Its nice because you can take it out, and hook it up in the house if you have a house unit, or other cars if you have more then one.
Satellite radio itself ROCKS! I hate listening to regular AM/FM radio any more, and I dont buy CDs anymore either. I cant live without my XM. My wife was like, "I dont need one, Im fine listening to the radio." Needless to say, that changed really quickly after I bought her the roady unit. She hates regular radio now.
Its worth every penny. Especially if you drive a lot, or live in the middle of nowhere like I do.
Any questions, feel free to ask.