Looks like there are three layers:
1) Close friends who've added new posts in the last 24 hours, then:
2) A couple of either REALLY close friends, or members of the opposite sex who are crushing on you, or your S.O. if you're in a relationship I suppose, then:
3) The latest people you added in order
And if there are no friends in 1) or 2), they're all from 3).
When you go to a friend's profile, it's different:
1) The top three friends that you have the most mutual friends with but are NOT friends with you (IOW, "people you may know")
2) Six others; mutuals if you have them, otherwise simply from the top of their Friends list