Which faction’s city do you like the most?

I would put the castle of the Sylvan and Dungeon factions in first place. I just can't choose a favorite; both are good in their own way. After them comes Necropolis, and the rest are all on the same level for me.

But if we're talking about the building that is constructed when you find the Tear of Ascha, then the most beautiful one is definitely the Sylvan faction's (Daughter of Silanna).