Assuming you are an artist, I think you have the wrong attitude concerning these social networks. I would think you would want to reach out through all venues. Nothing says you have to choose one over the other.
I use facebook but only occasionally. I see it as a place to locate old friends if you lose contact info. And perhaps once a month I take a look at what people are up to. Ping I did not plan to use much either but I do enjoy going to concerts. I figured Ping would be an extension to itunes store offering more information such as concert dates and meaningful updates from the artists. (Not twitter style pointless updates about buying new shoes).
I really do not understand why you, as an artist, would think you need to choose facebook over ping (or twitter or myspace, etc.). In pings case, since its within the application from which people buy music, I would think you would especially want that. Less time between viewing your material and purchasing means less time to second guess a purchase.
As I said in another post, I think Apple only needs to convince major artists to set up their pages in ping and all will fall into place with facebook cooperation. Established artists make more money with concert tickets than music sales so I imagine they will come on board.