1. Vanilla WoW: Since the upgrades they made to it during BC, Dustwallow Marsh has become one of my favorite zones. It has a very cool swampy vibe, tons of easy quests, and even an old school raid instance. It is also a very nice hub to get to the other places in Kalimdor. This zone used to more or less be a desolate wasteland with not a whole lot to do outside of visiting Tabetha for a few quests. They added Mudsprocket and a ton of other quests to spice it up a bit. Not to mention that it is the home to the dopest fisherman in Azeroth, Nat Pagle.
2. Burning Crusade: In BC, Nagrand was far and away my favorite zone. It may be my favorite zone in the entire game. It has absolutely beautiful scenery all around the zone. You also get to help out that crazy hunter Nessingwary wipe out the animal population yet again. The zone is full of lakes, green fields, trees, and awesome floating islands. There are even several waterfalls for your viewing pleasure. This is the one zone I always make sure to visit before I head to Northrend on any of my characters. The quests arent really the greatest, but it makes up for it in atmosphere.
3. Wrath of the Lichking: My favorite zone in all of Wrath has to be Howling Fjorde. It is just an awesome looking zone to me. I love the whole Braveheart/Higlander feel to it. The stories in the zone are decent, but the looks are what really get me. If you want some great lore, go to Icecrown and Storm Peaks. If you want a beautiful zone, Howling Fjorde is it. An honorable mention goes to Grizzly Hills which is a very nice looking zone as well.
What are you favorite areas in all of WoW. Where is your happy place?