At the top of the new Facebook Timeline profile, the 6 friends photos that facebook chooses for the smaller friends list box across the top banner is much more likely to show friends that are more likely to be your closer friends (and/or facebook stalkers, crushes, or recently interacted with friends). It's also clear that the friends shown are much less random "friends" and very much tied to interactions on facebook (recent interactions seemingly playing a large role).
So here are some factors contributing to why you might be seeing certain friends in the small Friends list box on your own profile:
- Interactions (recently and over time)
- Profile views (they've viewed your profile and/ or you've viewed their profile - Total amount of views when compared to other friends profiles viewed)
- Photos that you've been tagged in (or have tagged your friends).
- Wall posts
- Photos viewed (they've viewed your pictures, and/or you've viewed theirs)
- Online Friends who are currently Online (or recently been online for Random people that might show up)
- Chat - Facebook IM chat messages between each other
- Private messages sent between friends
Any "mutual interactions" between yourself and your friends will play a huge role, so if you and your friend both viewed each others profile recently (or liked each others photos, commented on each other profiles, were tagged in photos, etc), then these friends are more likely to appear.
Recent Interactions also seem to play a large role in which friends show up. As well as, interactions that have been on going for a longer period of time.
It definitely appears that Facebook has fine tuned their algorithm more precisely for the new Timeline profile friends "box" list, when compared to the older profile friends list sidebar.
The small six photo friends picture box seems to show friends facebook has deemed to be some of your closest friends and/or those friends most interested in you, based on their "facebook" interaction with you (and/or your interactions with them or each other).
Unlike the older friends list sidebar which seemed to have had more random friends show up more often, whom may not have been very close to you or well connected to you on Facebook, the newer Timeline profiles small 6 friends list photo box appears to show a lot less random "friends". While the friends pics will change more often if you refresh the page, these friends are much more likely to be "connected" to you on a more personal and/or facebook level.
So if you're seeing certain friends show up in the friends box, there's most likely a good reason for it... and there's a good chance that they are one of the following: good friends, family, facebook stalkers, your crushes and/or your recently interacted with friends.