I'll add my two cents. I've had a 2014 Mazda6 with Sirius Radio on a Bose system in it for 2 years. I let the 3 month free demo period lapse because I really didn't like the sound quality.
This past January we purchased a 2015 Nissan Altima SV with the regular (non-Bose) speaker system that had XM Radio in it. The quality was actually pretty good and it was acceptable to me. Still not as good as what I get at higher quality through my Google Play Music subscription, but good enough.
So recently Sirius/XM sent me a letter telling me they wanted to give me 2 free months of Sirius in the Mazda. Since the quality in the Altima was so good, I decided to take them up on the offer, figuring they'd improved the sound quality. However, upon spending some time listening to it in the Mazda, i can tell it sounds just as bad as the day I bought the car. It simply sounds like a low bitrate MP3, muddled, whisky, and sloppy.
In the Altima, which has no subwoofer and basic speakers, the XM radio sounds much better. I can tell the bitrate is much higher. I cannot believe Sirius/XM is still putting Sirus receivers in new vehicles. They should have started phasing these out a long time ago!
I am going to let the Sirius subscription expire and may keep the XM one in the car if the price is right. Granted, satellite radio is more convenient than streaming from your phone, and they offer a good variety of conetent for news, kids and sports fans. But with Apple Car Play and Android Auto hitting more and more new models, it is going to be easier and easier to stream right from the headunit. I stream from Google Play Music at 256kbps. It sounds glorious on the Bose system in my Mazda, unlike Sirius.