My personal favourite would be Mongolia. The war theme feels like a Mongol conquest of some city (I'd divide the song into three parts, the first one feels like the Mongols approaching, the second part is them sieging, and third is them sacking the burning city). The peace version is just out of this world. Civ VI Mongolian themes are trying, they are among the best in the game. They even have the throat singing and use Urtiin Duu again as the song they're based on, but they sadly don't reach the amazingness of Civ V...