Favorites of mine: Sholazar Basin Jade Forest Krasarang Wilds Stranglethorn Vale Silithus Winterspring Vashjir
Duskwood, Westfall and the Blasted Lands. They both have some really interesting environments, and I get a lot of nostalgia as I started out as a noob from these places long ago
I like Duskwood and the wetlands. I spend most of my lower levels in these places when I was just getting the hang of the game. Westfall is the nicest place, but there isn't much going on. At least not for somebody my level.
My favorite is Stranglethorn vale. I think that was in part due to the fact that it was accessible to both factions. Booty bay was an interesting area (I liked it better before Cataclysm). There was a lot going on in this zone which is why it makes it one of my favorite zones.
My all time favorite region is always going to be Mulgore. It's so lush, green and opened. The other area I like is Vashj'ir, especially one of the places where it's all purplish and white. It looks so majestic and beautiful.
Yea, always been a fan of STV. Perhaps it's nostalgia from the old days of world pvp, but it's always been a favorite zone of mine. The environment is really well done and its a great place to level a toon. I think nowadays, you can essentially stay in STV for 10+ levels.
Vanilla: Searing Gorge BC: Netherstorm WotLK: Sholazar Basin Cataclysm: Um. Twilight Highlands I guess? WAIT NO FIRELANDS Mists of Pandaria: Timeless Isle Timeless Isle Timeless Isle. It's one of the best designed zones of all time.
I like Stormwind forest and the region around Dun Morogh. Those are the regions I have the most memories of because I started there most of the time. I remember seeing the world for the first time and being amazed by the graphics because WoW was the first MMORPG that had decent graphics.