I'm p sure for myself I'd choose N's childhood, although I do think the dragons are quite close. The way I visualised it when they talked about it was kind of interesting and N's childhood would just enhance the games more, seeing that and then -now- in Unova. n____n
Everything else I don't have a large interest in tbh.
For the N's childhood one we could see like him being taken in for the first time and then time going by when N grows up and realises what he really wants to do for the Pokemon.