For me I'll say, in no order:
-Sylvan towns from HoMM5 (because it's an island of nature with sea view, what's more to ask)
-Dungeon (dark elf) town from HoMM5 (because the architectural style is amazing and I would think that there's quite a few interesting rock formations around)
-Anvil from Oblivion (nice quiet town, sea-side)
-Auberdine from WoW (nice natural city, sea side... though I liked it when it was actually intact)
-the sylvari city from GW2 (because plants and not so far from water either)
-the norn city from GW2 (because I like viking-like stuff)
-Nighthaven from WoW (because of plants, a clear nice lake and perpetual moonlight, while in the mountains).
I just can't decide on one and one alone