Hey WP!
Love my XM radios. (yes, more than one). I love the variety of programming that is available. I listen to news, oldies, pop hits, blues, bluegrass, classical, NASCAR, Jazz, old Rock... well, you get the idea.
I've heard a lot of people complain that they don't want to pay for radio when you can get it for free with an FM radio. I found it no different than cable or satellite TV. You pay for selection and variety. I have a mount in my car, in my office, and on my Harley.
I'm not sure there is any technological advantage of one system over the other. I don't think it's going to be like VHS and Beta where one becomes obsolete. I say pick the one that has the programming you like and go for it.
Joanne