Here's what I've noticed from my observations:
1. Any friends in the 'Close Friends' list, will automatically be in the top 9. Usually in the #1 spot. Put anyone on the top 9 list, under 'Aquaintances' and they will not show up in the top 9.
2. If you and a FB friend mutually have listed each other as a "family member" they will automatically be on your top 9, usually somewhere from positions 1-6, regardless of how much interaction you give them. But if you have a lot of interaction with them, they will move up.
3. Friends you usually mutually interact with the most will be in the top 9 list.
4. If you click on your 'Find Friends' tab(top right corner of your page when logged on FB. its between your name and Home.), you'll see 3 mutual friends listed under Mutual Friend. If you keep refreshing you'll likely see 9 different names--and that they directly from the top 9 friends box. Even if you put them under Aquaintance list, they will still show up on 'Find Friends' for a while.
5. Your top 9 list is directly related to the order of your friends in your friends list(for the most part). Almost all of them should come from the top 10 rows of your friends list.
6. People that you message/chat alot also has huge priority.
tl;dr version: I think All my top 9 friends are listed for a reason. Anyone listed as a family member or a Close Friend, automatically has priority. The people that you private message a lot, as well as people you generally publically interact with on a regular basis(comments, likes), i.e. your best friends should be in your top 9. IMO, I also definitely think profile and photo views has an influence. I just don't know if its one sided or mutual. There are 2 girls on my top 9 that I used to like, but I haven't publically(likes or messages) or privately(chat/pm) interacted with them for a long time,, especially my ex crush who's #3 now--whom I haven't had any public or mutual interaction since last July.