The combination of Spotify, LastFM and Facebook is far better and more promising than Ping, because it allows you to stream and thereby listen to music without buying it = you can share a lot more with friends. Ping is not made for the users to share, it's made to sell music.
The big draw for MySpace is the ability of unknown artists or bands to get their music heard. Yes, youtube can do that too with channels but MySpace isn't much more about the music than music+video which is what youtube does well. Ping doesn't do anything to help up-and-coming artists and bands.
I personally don't like MySpace and only use it to check out lesser-known artists.
As for Ping, by itself, the lacking ability for iTunes to automatically track what you listen to most and add that as your "followed" artists is a huge issue if you ask me. What is this? Winamp? Where you have to manually do your own musical tracking?
Let's see what happens with subsequent updates to iTunes...
Currently, Ping does not have any support for the artists (indie) and makes it difficult for them to use the service to reach out to fans. Also, it is - presently - a dead end with no means to share updates with major social networking services.
Although MySpace is still not perfect, they are doing a better job right now...especially with the recent revamp of the UI.
I do hope Ping gets it right soon.
Ping is too new and it so empty Myspace have way more users and Artists then Ping have so I'm with Myspace on this one