A friend of mine mentioned this comparison of the two systems,
Differences
Sirius is 100% commercial Free on ALL of their music channels
XM is not with now up to 6 minutes in commercials an hour. When they started they had a maximum of 2 minutes an hour.
Regular radio averages 22 minutes an hour.
Sirius has 3 satellites vs. XM's 2
XM uses more repeaters because of the orbit of their satellites
Sirius has a variable bandwith for each channel / XM is fixed
Sirius has original programming / XM rebroadcasts their music
Why pay for something you can already get for FREE!
It is true that both services have far superior sound quality than traditional radio.
XM is WAY ahead with subscribers compared to Sirius (XM owns 85% of the subscribers to date). XM executed better than Sirius has and launched their service a year in advance. Doesn't mean that Sirius is out of the game. Sirius's OEM partners are just now coming on board. Ford and Chrysler along with everything under those mega umbrellas (Range Rover, Jaguar, Jeep, Dodge, Lincoln, and Benz to name a few).
Put it this way, BMW could have had satellite radio (XM) over a year ago in their vehicles, but waited and signed an exclusive contract with Sirius. There is a reason for that. Do they know something that we don't? Why did Ford and Chrysler wait so long to have satellite radio as well?
They too have exclusive contracts with Sirius. XM has GM and Honda. Audi/VW/Nissan/Infiniti have dual platforms meaning you can get either service. Toyota will offer either as well.
This game has just begun and is far from over. Both companies have secured good funding for a few years so it is interesting to see what happens. My opinion is that there is room for both companies and they are here to stay.
BTW, he had 2 XM systems and recently switched to Sirius for the better programming and no commercials!