I voted for Greyhawk and Birthright.
I was tempted to also vote for Dragonlance, but I have a weird relationship with Dragonlance. I love the original books, but something about the presentation of it in D&D 3rd Edition (the edition I started playing with) didn't click for me. Also, there's a certain point beyond which the novel lines changed the world enough for me to not like it as much anymore. So, I love the original books, but not some of the newer stuff. Gamewise, I actually do like some of the aspects of the campaign setting as shown, but typically use those aspects in other settings without using the DL setting.