fav is northrend in general or netherstorm. but i detest the rest of outland. hate it, hate it, hate it. needs a huge assed mana bomb dropped on it to remove it from the world
My first toons were Alliance and nostalgia definitely factors in. Also, before BOA leveling gear, they were actually decent challenges for your characters.
As you said, Nagrand. It just gives a peaceful feeling yet it's beautiful and epic. It was my favorite zone the minute I stepped foot in it and has stayed that way through many xpacs.