I will be the one to attest I have both services almost 3 years now and will give you my opinion.
XM's music library per genre' is the largest but their sound quality over satellite is starting to suck more as they changed the codec which makes it sound more tinny with less Bass and I need my deep Bass & high Treble notes.:rockwoot:
Sirius has a wide selection of Rock channels with slightly better over the satellite sound quality but the rotation of songs is very repetitious.
For the online service both offer at no charge to the regular subscription.
XM's sound quality is hands down the best as they upload at 64kbps which is about CD quality.:rockwoot:
Both have excellent receiver options.
Come later in the year or early '08 they(if the merger goes thru) will offer al la carte programming;
50 Channels you select for $6.99 a month per receiver
Or the Everything Pak for $15.99 or $16.99 a month per receiver.
I'll go for the 50 Channel option so I can have all the Rock channels of both:rockwoot:
Stop in at a Best Buy or Circuit City as they usually have both hot in the audiophile rooms so you can try em both out on different receivers,amplifiers and speakers
I want to say over Satellite Sirius has a slight edge sound quality but not by much.Is that supposed to say Sirius sound quality is best?