I'd have to go with Khenarthi's Roost. I loved the beauty of the island and the Khajiiti architecture, both the ruins and the city of Mistral. That is partially what made me love the game even back in the beta; and boy was I a harsh critic during the beta.
Otherwise I would have to say Rivenspire, the Gold Coast, Hew's Bane and Auridon all based on looks. The content in each was fun, but what drew me to them was their looks.
The Rift - I'm not sure why, I just love the atmosphere of this place. It calms me down just to run and collect mats in there.
Vvardenfell - duh, it's so beautiful and unique, love the shroom crabbies
⊂( ̄(工) ̄)⊃ Don't-Care-Bear ⊂( ̄(工) ̄)⊃
PC EU "House Tertia" - Friendly Guild for Mature Folks (housetertia.com) PC EU "Priests of Hircine" - Awesome Guild for Friendly Werewolves (free bites!) Master Angler
Craglorn, beautifully designed. Some zones and group quests are really a piece of art. Other very well designed zones are also Vvardenfell (Public Dungeons and Delves are very interesting and fun) and Wrothgar (it reminds me of Skyrim). I also like the setting in Coldharbour
Rivenspire for its grim and dark atmosphere
Wrothgar for its incredible detail
Craglorn for its higher difficulty, sense of adventure, loneliness, and fantastic delves/dungeons.
Not in any particular order, but Alik'r Desert, The Rift (one reason being that Riften was my fav city in Skyrim), and Greenshade. Oh look, one for each alliance, lol
PC - NA
CP 1125
Veric Blackwood - Breton Magsorc DC
Xhiak-Qua'cthurus - Argonian Frost Warden EP
Kujata-qa - Khajiit Magplar AD
Suunleth-dar - Khajiit Stamblade AD
Teldryn Antharys - Dunmer Flame DK EP
Strikes-With-Venom - Argonian Poison DK EP
Rur'san-ra - Khajiit WW Stamsorc AD
Ilianos Solinar - Altmer Stamplar AD
Iscah Silver-Heart - Reachman Magden DC
Vvardenfell, and Glenumbra (Daggerfall). Mostly because of nostalgic reasons. I started my Elder Scrolls adventures with Morrowind, so Vvardenfell comes to me as a natural homeland. However, I also went back and played the first two, as well as Oblivion then eventually Skyrim when it came out...
And I gotta say this. Exploring Glenumbra, especially the town of Daggerfall, brings back nostalgic memories as well due to the music. There are some music that plays in the town of Daggerfall were are either directly ripped from the 2nd Elder Scrolls game or some sort of remaster version of the song.