1. Grizzly Hills and Howling Fjord.
Why? Simply because of the northern feeling. The music, most of all. The Vyr'Kul. The looks. Because I get a massive dose of nostalgia evertime I simply think of it.
2. Durotar and Mulgore
Again, nostalgia. The music. Memories of starting WoW, the blissful days of being a newb? Sound cheesy. But true.
The looks. The colours. The floatig rocks, the vibrant fungus. The cascades of sparkling gems. The story. Saving the world 'n shizz.
4. Storm Peaks
The music. Titan lore (loooove eeeeeet). The music. The lightning, thunder, stormy mountains. And oh yeah, THE MUSIC.
5. Jade Forest. Krasarang Wilds. Nagrand. Vash'jir. Zangarmarsch. Thousand Needles, and so many more.
Here it gets hard. There are so many more great zones but I dont have time to write about all of them (I dont mean that to sound pretentous). The matter is subjective ofcourse, but I believe the ones I have listed among many more are fabulous zones and we saw with Pandaria that Blizz is still making awesome ones. My two cents.