I like Felwood and Winterspring, its two great zones and the road to 60 is almost over. I played Alliance in vanilla so Elwyn Forrest, Westfall, Redridge Mountains and Duskwood has a special feel for me. This time im going to play Horde and pay some new (hopefully) awesome zones.
Tirisfal Glades and Silverpine Forest, I enjoy the atmosphere of the Undead leveling zones a lot. Looking forward to giving Hillsbrad Foothills another try as well but it did not make as much of an impression on me as the zones that came before it.
It's gotta be Feralas. Exploring as a lvl 46 hunter and suddenly stumbling upon an elite dragon named Emeriss. Filled me with awe. Been fond of the place ever since
Ashenvale floats my warcraft boat. It just has a great feel to it!
Tirisfal Glades. I like the fast and easy leveling of the 1-10 zones, and the fact that the questing experience is self-contained. It doesn't have quests that send you to 3 other zones to start 3 new quest chains when you're not even done with the zone you're in. It doesn't have you bouncing between two quests hubs like Durotar and Elwyn Forest do, and it has better access to the faction capital than Mulgore and Teldrassil do. Many of the quests feel related to each other, like different steps in a cohesive campaign. And it has that dude on zombie island.
For me:
Overall - Swamp of Sorrows
Horde - Silverpine Forest
Alliance - Dun Morogh
Teldrassil is probably my favorite place to quest, it feels like home.
Westfall has big place in my heart too.
Redridge! I love the autumn theme of the zone, and the fact that it has a lot of different mobs and also contains my favorite hub, Lakeshire.
Hinterlands. I love its tranquility and the open-world "mini-dungeon" Jintha'alor stands out from other leveling zones.