Personally, I think it should be Oz. An Emerald City raid is what the Grimoire card Fallen 6 implies, and would be really fun.
Some Other Options that Didn't Fit in the Poll:
-Planet of the Apes
-Las Vegas
-An IKEA
-The Capital Wasteland
-Orgrimmar
-Nirn
-The Soviet Union
And last, but not least:
-Tuchanka
-
Lost Guardian Clementry. Where you pay your respect for fallen guardians