Firstly sorry for any grammatical error in the title, it's not something easy to literally translate for me :D
What is the zone that, looking at screenshots or video about it, makes you want to play again? The one that makes you say: "Oh, I should play again to some Wow?".
I don't know if I'm able to explain myself, it's a different feeling from your favourite zone. It's more the zone that, for you, encapsulate what you love mostly of the game.
For me is probably Alterac Mountains: a zone with no horde outpost, a lot of elites, some cool quests and rare vendors to be found. I find it emblematic of the game itself.
Hydraxian Waterlords - RP - EU
- Fendor - Tauren Shaman
- Ildebrando - Dwarf Hunter
- Osandiron - Dwarf Priest
That would be Hillsbrad, it was my first time encountering a lot of alliance (or so it seemed to me), and the corresponding wpvp, and just the general feeling of being unsafe.
For me that would be Duskwood but I'll be rolling Horde this time, so.. 
Other than that, I really enjoyed WPL and EPL.
I used to play Warn, human mage on The Maelstrom EU <Ashbringer | Rachell's Angels | Entrophy | Relentless>
My first ever character was a human, so hearing the Elwynn Forest music brings back a flood of great memories. But I play Horde now, and the Barrens are just so iconic, so it gets a mention too.
Literally everything but Desolace 
The Footpad
Elwynn, Westfall, Duskwood. Such a dope combination.
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couchatron • Henhouse • Code • beached • Alnir • PhillyOutty
At this point I just want to play again so I could rediscover each and every zone.
However, I was always particularly fond of Mulgore, Ashenvale, Hillsbrad, and Azshara, so those zones would bring about the most nostalgia.
Westfall for sure. Stranglethorn Vale is also amazing to quest in. But I really just love Westfall.
The Plaguelands, Western and Eastern.
I forget who the quote was from, but I remember reading in a Duke Nukem 3D Level Editor guide when I was a kid some tip that a fun level design tip is to let the player see into an area they don't have access to yet. I think having it connected to one of the newbie zones is kind of the MMO equivalent of this. You can walk in there, but you'll immediately get your ass kicked by a plagued bear or something. It sets it up as something to build toward. Kind of gives me the same vibe as the boss statues in Super Metroid, if that makes sense.
Mulgore into barrens into thousand needles! I always favored Tauren, and spent so much time there. I'm still bummed what cataclysm did to some of my favorite zones :(
Funny enough, since it was named Desolace i didn't really mind it. If they had named it anything else, I might have been miffed.
Teldrassil. First zone I ever set foot in in the world of Azeroth and man was I captivated. I'm still in love with it -- the music, the ambience, the scenery...that zone is a masterpiece.
Fun fact: I got lost in Shadowglen the first time I played; I couldn't find my way out :P
Yeah definitely this, Mulgore into Barrens, playing into the night and watching the starry sky as I made walk into southern barrens from Crossroads..I really look forward to that again.
My most nostalgic zones are definitely Elwynn and Teldrassil, but that's because I played Alliance in actual Vanilla. Those are the zones that really hit me in the feels. But I want to change it up, so I'm going Horde this time. Not much of a nostalgia factor, but a different experience.
So I guess other than that, Hillsbrad! Southshore vs Tarren Mill, good lord, those were great times.
Walking up to the gates of IF for the first time and seeing how massive it is as the soundtrack starts to play. I love it, and its a big part of why im rolling a gnome.
Oh I loved Tanaris, felt like you've really progressed in the game once you get there.
Dun Morogh and Elwynn forest get me every time.
Probably all starting zones? Just hearing this familiar voice and looking over the zone and that finally getting control over you character? Iconic.
Besides those: Tanaris.
Like @Grozlam, The Plaguelands, Western and Eastern.
I have a thing about murdering scourge filth, I just wish there were more mobs to kill. I've never seen the scourge invasion, that's one of the events I'm eager to see in the flesh.
Have you played Vermintide [2]? It's the same feeling, you're just getting rid of the baddies around, doing the right work.
I love everything about the barrens until I have to collect the supply boxes from the stupid quilboars...
The Footpad
Darkshore, reminds me those times i play wow for first time as NE male warrior handing around with no mere goal, although it was on TBC but still...
Mulgore, Dark Shore, Thousand Needles, Tanaris, Wetlands, and Duskwood. Every single time. Bonus zone for me is Moonglade, I miss playing my druid in Vanilla!
