Sirius vs. XM

Hey, Im looking for some opinions from those who have or have used both systems. Im getting conflicting reviews but usually only from those who have only used one or the other. If you have tried both systems let me know what you prefer. Im leaning at this time toward the Sirius radio because of Howard Stern and the NFL. Who has the rights to Nascar?

right now XM has NASCAR but in 2007 Sirius will have it

http://aftermarket.autoblog.com/entry/1234000613033572/

http://www.streetsourcemag.com/Forum/topic.aspx?method=reply&topic_id=68162&forum_id=35&forum_title=&M=False&S=True

^^Already had this discussion, I went with SIRI.