I prefer Facebook. It's for a more mature crowd. Users aren't allowed to edit their pages in ridiculous HTML code. It has a more professional feel to it. Users aren't using retarded ass aliases. It's simply full legal names. It does not have spam like MySpace. Plus, everything MySpace does now is catchup with Facebook. They stole the tagging ideas. Along with the news feed.
It's more professional, but I fucking hate 99% of the apps.