Just a comment on Last Exile, I haven't watched Fam yet, and although I agree it was inconclusive , based on just the first anime Tatiana in my opinion was the most likely pairing with Claus, which would mean Childhood friend loss.

But I kind of do agree with this thread that contrary to popular belief, Childhood friend is almost as likely to happen as first girl wins.

Actually, one thing I'd like to see is a comparison that takes into account separation. That is, rather than just how close they are at the time of the story, include things like periods in which the two were separated. At least from my perspective this as well as the closeness/openness of the friendship have a big impact. A childhood friendship where the pair have always been together, practically inseparable, since early childhood, with both parties trusting one another absolutely, chances are very low: if there are any real rivals it won't work out. If one of the two is always distant, sort of tsundere, full of walls that don't let the person close, there's a fair chance, but it's still relatively low. On the other hand, if it's a childhood friend the MC hasn't seen in years, or one from so long ago that they don't even remember each other and the connection comes as a sudden surprise, chances are very high.
Thus I think it'd be cool at some point to compare these characters' separation, from "closer than brother and sister" to "friends but with significant friction", "best friends but somewhat distant for 1, 2, etc. years", all the way to "met long ago but completely forgotten".