Realistically? The zone with most animal farms. Elwynn Forest probably reeks of pig and cow poop.
I always think Maldraxxus must stink
It’s all just sludge, goo, decay and yick.
I often call the horde capital “smellytown”, though I have to agree Maldraxxus probably smells even worse.
Eastern Plaguelands 
I guess it has to be Undercity - my undead frost mage has a green tinge and whiffs 
Has to be undercity. Becuse its underground and no fresh air.
Maldraxxus, easily.
As scourge zones have been mentioned, there are also zones infected with demons. I imagine fel is like sulpher - rotten eggs.
Also, Nazjatar probably reeks of fish.
Not sure what void would smell like but I keep thinking red wine 
Burnt electric wiring/circuit. 
Maldraxxus is what comes to mind. Lots of rotting flesh, rivers of scourge.
Maldraxxus. I remember when I quested there for the first time it was a very nauseating experience for me, literally.
I would guess Maldraxxus! It smells so good! 
Maldraxxus and Eastern plaguelands.
Once Undercity… But we cleaned out huge toxicity from Lordaeron ago.
Maybe Lordaeron/Undercity no anymore smelly
I reckon Zandalar is probably a bit whiffy, all those bare feet in a hot climate and you don’t see any showers anywhere… also they allow dino’s in the city so I imagine they add to the ponginess regularly 
Thunderbluff definitely stinks, given what cows tend to smell like on warm days.
I’m also personally convinced that Undercity and the undead smell like sweaty feet.
Your name updated!
I tried logging in and out and that seemed to work! Huzzah!
It would probably smell worse if they wore socks and shoes, at least they let them breath.
Stormwind. Followed up closely by all other Alliance capitals, villages, and zones.
