Hard pick, but currently I'd probably go with Yi. Beautiful tiny wyvern.
If there were ever non-pterosaur flying reptiles added to the aviaries, it'd be nice to have a Yi or a close relative. Would need to be scaled up though, because they're really small.
For animals in the game... I gotta agree. Quianzhou is neat. It's got everything that made me fall for Alberto in the first game, and more.