I honestly can't pick most favorites and least favorites, because I enjoy each zone yet could probably find something about it that I'm not crazy about if I want to criticize it. Also, my time spent in each zone can vary a great deal from week to week. So the following is not meant to be definitive in any way.

Vvardenfell -- This was my introduction to TESO, and it holds a great deal of nostalgia for me for that reason, as well as for its emotional connections to TES III: Morrowind. It's where most of my characters are parked, except for a few who are parked in other zones for questing purposes. My biggest nitpick about it would be that the Red Mountain and Sheogorad regions aren't accessible.

Glenumbra -- I think this was the third zone I visited, by taking a boat from Vivec City to Wayrest while trying to turn in my daily crafting writs. (The way I remember it is that back then the quest pointers for turning in my daily crafting writs were pointing to different cities in the Daggerfall Covenant alliance zones, such as Wayrest and Shornhelm and Daggerfall, although I'm not sure why that would be unless it had something to do with my crafting levels in each of the crafting skill lines.) Once I arrived in Wayrest, I followed the quest pointers westward into Glenumbra. I was so excited when I finally reached Daggerfall, due to its connection to TES: Chapter II - Daggerfall, even though I hadn't yet played that game at the time. I love Glenumbra's lush greenery, and can't think of anything noteworthy to nitpick about. Later on I decided to park my main character in Daggerfall for several months for doing daily crafting writs and just getting to know the zone better, and my primary housing on PCNA is there-- Captain Margaux's Place, which is cozy and conveniently located. I own nearly every player housing on PCNA, but that little house is where I put my transmute station and standard crafting stations, along with my assistants, so I go there often.

Alik'r Desert -- I've never lived in or near a desert, but I love the whole desert vive here. But most of all, I like how there are so many Dwarven delves in this zone. It also has Volenfell, which was the first dungeon that I ever soloed. I never tire of soloing that dungeon. Aside from the nonstop dolmen train (which I very rarely join in on), there are at least three locations with a lot of zombies for players to kill when they're farming XP to level up their characters.

Cyrodiil -- Aside from any PvP considerations, I love Cyrodiil and how large it is. There are a lot of delves to explore, and while they aren't as fancy as the delves in later zones, most of them have more than one boss to kill. It can also be enjoyable to do the daily town quests, although in some of the towns the dailies can be problematic to pick up and turn in. Scouting missions can be fun to do if a player is new to Cyrodiil and wants to try to avoid PvP, and sneaking carefully from one side of Cyrodiil to the other can be a great way to become familiarized with the landscape, learn the impassable places and where to go to gain access to each third of the map, and discover all of the little scenarios which dot the landscape, such as refugee camps, old picnic spots where bad things happened, or destroyed and abandoned houses. But once I lost my fear of getting killed in PvP and discovered how much fun (and frustrating) it can be to capture or defend keeps, these days I mostly go to Cyrodiil to earn some AP by capturing resources and hopefully getting into some XvX battles where my side isn't terribly outnumbered or just too outclassed.

Imperial City -- There, I said it! I used to enjoy doing all six daily district quests as a way to quickly burn up any large amounts of enlightenment that I'd accumulated, but I'm currently doing just a single district daily (to earn a Siege of Cyrodiil Merit) and then heading into the sewers to farm TV. I acquired all of the skyshards years ago, and have killed all but one of the stationary bosses in the EP section, but apparently there are still discoveries to be made, such as lore books I'd previously missed. I also need to branch out into the AD and EP sections to become more familiar with their layouts and get better at fighting all of the stationary bosses, some of which I've only fought once with other players of my alliance, although I did solo several of them back when I was trying to clear the zone map.

I will group some because I feel they're complete together:

Favs
1. Elsweyr, North and South
An obvious choice. Zone story was awesome, from prologue to epilogue, love the lore, khajiit, ancient dragon hunters, Tharn, etc. I remember my head exploded first time i confronted a Dragon in The Demon Weapon, even if its scripted win. I was at my peak on hype within ESO. Landscape-wise another win for ZOS: Love the Stitches and canyon-like structure from the middle, the northern more Savannah and Southern more tropical forest, which leads to south elsweyr and the coast, and Tideholm. All lovely. Also Sunspire. I also love the feeling odf everytime you face a dragon you gotta cross one of those bridges, like a prologue to the fight. The only thing i dont like here is the empty gap between north and south on the map.

2. High Isle, Amenos, Galen, Yffelon
Put all those together because they're all alike. While I like most of the Zone's Story, was expecting more for a "more political plot", but liked the epilogue on Yffelon, the Maormer and the druid stuff. Landscape-wise beautiful, love the contrast between forest and lava in Galen, all the druid settlements and the general classic medieval fantasy of the bretons. Vastyr is my favorite city of the game hands down. Love the uniqueness of ESO druids ams their lore.

3. Clockwork city
Someone said above the otherwordly feeling here. Just awesome. I just wish it was a full, bigger zone. The steampunk, mechanjcal ambient are all very good to me. I have the same feeling from Corpus Facilities on Venus in Warframe. The story was awesome too, my fav quest in the game where you help the crows and the final Seth's talk, Fyr, very nice. Halls of Fabrication should belong here...

Disliked
1. Blackwood
Most of the area are feels very very generic. Was expecting more swamps, which start to appear south, but just a small part. They could've explored more the longhouse emperor's lore but it went quickly to Oblivion lore...When it goes to Oblivion it turns the super cliche good vs evil. Also hate Eveli, dont like her character at all. Its associates dungeons feels very much the same for me, fire everywhere, tho i like black drake villa and red petal lore.

2. Stonefalls.
Not much to say but the zone feels very depressing for me.

3. Apocrypha
More lore enriches the game, which is always nice. While i find interesting the aspects and thoughts around Knowledge within Mora, this isnt much for me. But I like its here.

Honorable mention
I am very fond of The Rift. While I find its zone story weak for the most part for a final zone, I played through it by the ens of a year with all Christmas vibe. The loading screen art grew in me as a very good nostalgia feeling towards it. Its snowy but not so much. Every year near Christmas I remember that zone.