For me, it was Maia, then Sari. I was kind of confused at the idea of not marrying Maia after finding her was the whole point of the first generation.
I then went with Sari because a) Ayn and Thea are cousins, and that seemed weird even to me as a little kid, and b) Sari is a badass (unlike her very weak mother - who was her dad, Re-Faze?)
I thus ended up with is probably the hardest third generation (not quite as long as Sean's, but Crys lacks healing techniques, as does Warrior Kara. The difficulty level is relative, though, because none of them are actually hard).