Have Sirius in my 04 Mach 1 because it came ready for it, though they had to install the tuner under the seat & have XM on my other car though not ready for it the unit has a small faceplate with the tuner hidden under the dash.
My observations:
Sound quality goes to XM
Programming about equal
Technical problems such as losing signal where the service has to be called to send a signal Sirius is worse, had to call 4 times in 1 month so far no calls to XM.
Customer service goes to XM, Siruis is horrible, anything wrong they blame the unit including Sirius has a $75 cancellation fee if you take one of their plans but customer service does not tell you about it when activating but will say they did.
My conclusions:
Will cancel Sirius when my prepaid year is up & go to XM with the add on unit.
Anyone thinking of Sirius like I did because it is built into the head unit think again because XM is better totally & with the small units from XM no advantage to the Ford headunit.

 

XM is by far better then Sirius. XM is more widely used then Sirius is also.

 

You definitely have that right, XM has better sound & seems like a much better company. Sirius customer service is pitifull.