Ive had Xm for a little over 4 years now ... I just put Sirius in my trans am yesterday.
I have 4 xm recievers.... 
Starting with the oldest.  The Pioneer headunit thats in my truck (used to be in my old ranger).  I have like the GEN 1 tuner box for it too, but still sounds excellent.  Thats in the second picture on the right.
 
 
Then I got a SKIFI2 that I take everywhere.  I got the boomboxes for it (one im modifying right now with bigger speakers), car kit which i put in my work truck when i take long distance runs, and the home kit which is pictured.  Thats in my spare room...
 
In my bedroom, I have the Polk Reference XR12 and it soudns the best.  No digital compression can be heard at all.  I like it, little pricey though....
 
Then I got a delphi roady 2 thats in my dads truck.  Its cheaper that its on my plan so instead of him paying 12.95 a month, its 6.99 a month.
Finally after yesterday of having terrestial radio in the trans am, I signed up for sirius.  To tell you the truth, I like the rock selection better then XM.  I just hate Howard stern.  The Sirius tuner is mounted under the passenger seat, and I had to use double stick tape to fasten the antenna on the roof.  Damn fiberglass cars ... lol
 
Satellite radio is cool ... lol