I’ll always love Zangarmarsh and Nagrand. I was so anoyed when I hit 70 on my Dracthyr Shadow Priest and Chromie was like: “Lmao, fun’s over, go do the War Within campaign now, scrub!”
Mmmmh… Weirdly enough I still love leveling in BfA zones. That’s usually my go-to if I’m starting an alt from scratch.
So I guess that’s my answer: The various BfA launch zones.
But there’s loads more zones I love. I’m mostly a world content player for a reason. 
Heirlooms are the answer. 