Wow. 9-2. Just wow. Early lead, I wonder what it'll look like tomorrow morning.. this morning.. later..?
It's no surprise that Planescape will win.
I think that is the direct result of the collection of persons who frequent this forum/site. There is a vocal unabashed fanbase for it here.
I do not think, necessarily, that translates to it being the most popular setting in D&D TTRPG fandom as a whole.
I voted Greyhawk...but still expect PS will ultimately win.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.