We have both. We've had XM since their beginning. We have multiple receivers for both too.
XMs:
3 Delphi receivers (original plug-n-plays) (1 is put away and doesn't have service right now) - we use these in dh's car and the boom box that stays out back under the patio.
Roady II - in the mini-van
Inno - I got that for dh as a birthday present last year
Sirius:
Plug-n-Play and portable boombox - this was dh's birthday present this year so he could listen to NFL games
The second Sirius came equipped in the van. Our free 1-year subscription ran out but for some strange reason it started receiving programming again about a year later.

We don't even listen to it. I realized it one day when I accidentally flipped to that mode on the radio. I don't like it because I don't get the display info about what is on. Another thing is when we first got the van, the Sirius receiver didn't operate properly. Again, for some odd reason it works everytime I accidentally flip to it now.
My favorite channels are 202 - Ron & Fez; 155 - Dr. Laura; 40 - Deep Tracks; music channels - 20, 21, 26, 29, 30, 47, and 54. I used to listen to E! alot because I like the E! True Hollywood Stories, but now everytime I flip to that channel it is some show called Yo! on E!.

I don't listen to Sirius.
Dh listens to XM mostly. He listens to Sirius on Sundays for the NFL games. On XM he likes O&A, Ron & Fez, the political stations - both conservative and liberal, and he listens to alot of the music channels.