Originally Posted by moonpie

XM came with my GMC Sierra when I bought it, and I'm happy to say I like it. However I have a friend who has Sirius and I ride with him a lot.

Your main concern is reception. XM covers all of the continental US, while Sirius does a figure 8 type formation (leaving out certain parts of the midwest. )

Reception with either one in a metropolitan area is good. But if you travel back roads, long stretches of highway, or live in a non metro area you have problems with Sirius. Audio quality, regardless of what anyone says, is about the same, however XM does have a slight leg up on Sirius (however Sirius recently bought the company that produced their encryption and ripping codecs, and audio quality is improving).

I'm not sure about Sirius, but I know all of XM's music channels are commercial free.

Now I'm not sure if SIrius does this, but I know XM plays a lot of artists that aren't being played on regular radio stations (aka Clear Channel owned or operated). Plus XM has more stations than Sirius that don't censor the lyrics (atleast for rock). The DJs are awesome for both and in all likelyhood you can listen for hours on end without hearing the same old loop! (atleast thats been my experience with XM)

XM is better IMO, but you have to see what both offer in terms of stations. Find somebody who has Sirius or XM and see what you like on there.

-Edit-
Also, look at the pice for service. I believe Sirius is $14.95 a month and XM is $9.95 a month. Both offer discounts if you get multiple years of service (like 2 yrs for the price of one and a half)