Xm have only 2 satellites orbiting the equator, whereas Sirius have three satellites orbiting in a figure 8 pattern, which I am sure means better reception coverage. I picked XM only because I liked the size of the receiver which is smaller and looks nicer than Sirius, it has the orange background lighting which is identical to the 740iL dash/radio lights, the antenna is a lot smaller than Sirius and is barely noticeable. Also the monthly fee for XM is $9.99 whereas Sirius is $13.99 and is cheaper the more years you pre-pay eg. for 5 years I think it worked out to $7.50/month. I also had to pick one that worked in Canada, as it is not available here, and I knew a few people that have XM with no problems!! Anyway I hope this helps, but I think it is all personal preference as the programming is fairly similar(more NASCAR on Sirius). Good Luck. Nigel