I went with Scarred Lands.
First setting, aside from the upcoming Ptolus, built for third ed, and the first setting to really try to integrate and make sense of its DnDisms:
sorcerous blood, armor less mages, monks, and so forth all found good homes in the setting.
I thought that in that regard it was superlative.
Edit:
All right I went back and reread the original post, and I have to say that I see reall disconnect between what it asks and what the poll asks.
In that case I'd probably go with something like Blackmoor or City State of the Invincible Overlord, but honestly I think it's a pretty silly question.
The whole purpose behind my picking Scarred Lands was that I thought it was well tailored to the rules. If we're getting new rules with new data then I want a new setting.
The only advantage to Greyhawk in the first place was that it was steeped in arcane DnD lore but fairly generic, if you were to pick by that criteria then I'd just as well say you should go farther back.
Then you get a load of arcane trivia and easter eggs, but it's also far enough back that you don't step on anyone's toes as you did when you 'lightened up' Greyhawk.