OP
you can go online and try out each company. i know for sure sirius did this. i was gonna get sirius but i got xm for free so i took it. if you got to http://www.sirius.com you can get a free 3-day pass to listen to sirius on your computersee now i have no idea which one to get.....
They are the same price, sirius also has online access, and better selection/more diversity is a matter of opinion.XM FTW!!!!!--- XM = better selection + More diversity + lower price + free On-line access to ALL of their channels with your subscription. you have your music that you pay for with you when you are at home or traveling in the car. The xm unit that goes with your Alpine can be hidden away under a seat etc... safer, less components in the open for prying eyes.
I went with XM when I was driving long-haul... my bf went with Sirius.... and he seriously HATES IT!
XM > SIRIUS!!!!