I don't care whether I hear Stern or not. Having said that, I haven't any of the problems others have had with XM radio. Neither has my gf or best friend. Occasionally, if you use the FM tuner, you may have a bit of static if you don't have it set on an unused station.
I have had no experience with Sirius so I cannot comment. However, when they first came out, I had decided on XM due to stations, etc. That may've changed by now. I'm just hoping they merge then I won't have to worry about it.