I'm personally more intrigued by Sirius than XM. For one thing, Sirius is going to have a CBC Radio Three channel, which is something I've been wishing for since, like, forever. (If you've never checked out the CBC Radio Three website, it's fantastic. Probably the closest webradio's ever gotten to capturing the old-CFNY spirit without pretending music ended in 1989.)
Capturing the old CFNY spirit, for me, isn't about a radio station doing 24-hour alt-retro; that has its place, but it would get boring real quick if it were all a station did. I want a radio station to be adventurous in introducing me to new music I haven't heard yet. Sure, throw a few old favourites in the mix, too, but gimme my Arcade Fire!