Actually, the three city-states culturally dominant Clans are Sea Wolves in Limsa Lominsa, Dunesfolk in Ul'dah, and Wildwood in Gridania. Midlanders are the most populous because they're common everywhere, but they actually lack a defining culture. They tend to blend in with the local culture, save for traditions related to one's personal life and family, such as marriage, funerals, naming and so on.
At least, that's how it looks from my observations.
At least, that's how it looks from my observations.