I hate myspace just because the interface is terrible, and the ad's are even worse. There is aton of span and corporate crap that ends up there, as well as the 10 year olds of America.
Needless to say, I still have a Myspace account.
Facebook however, in my opinion is a lot better. The interface is clean, you can upload all the photos you want, and developers can make applications that run in your profile, that are really cool. Another great feature about facebook, is that if you have an interest, you can add it to your profile, and search for people in your area with the same interest. So I can easily find people into "Computers" "Phreaking" or "Sex with grapefruit."
Facebook is especially useful for those in High School or Collage, because you can "Join" that Network, and easily find and talk to everyone else who goes there.
Cons with facebook is that myspace is more well known, therefore more of your friends might be on it.
Hope this helps,
And RBCP, WILL YOU BE MY FACE BOOK FRIEND?