I still say the Srivijaya/
Majapahit Empire (basically ancient Indonesians with a large advanced empire) would be awesome for the cultural diversity (on Earth maps, normally no one starts in Indonesia), they're just as relevant as the Incas or Mayans the only drawback is no one's ever heard of them

(Hell, Kublai Khan even sent an invasion fleet from China trying to conquer these guys and got his butt whooped)
Other than that my vote goes Inca because they are cool and someone needs to start in South America on Earth Maps.
Spain, Korea and Vikings would also be nice.