XM is way better.
From my experience XM has much better play lists for their Rock, Rap, Country, Oldies, Kid Stuff, and Seasonal (Christmas stations).
Sirius has gone out on a limb and paid Howard Stern way too much money, 0.5 Billion, and put all their eggs in one basket. Howard is over 50 now and, most are saying he is going to have a hard time keeping his