Really liked Greyhawk, though I rarely got to use/play in the setting. Wasn't that crazy about the blow-up due to Greyhawk Wars, but I enjoyed the setting. Glad Vecna showed up again.
I liked Mystara for the OD&D/"Red Box" style D&D, but I wasn't keen on it for AD&D.
I liked the way that FR was before 2nd ed. and a lot of the tie-in novels/trilogies/series were introduced. Just a basic setting with good flavor. The Time of Troubles, spellfire, wild magic, Chosen of deities, & lots of other stuff just flat-out killed the setting for me.
Dragonlance seemed to epic-bound to me--there was always a comparison to the books, in my mind. Hated the way players typically roleplayed kender, not to mention the Raistlin wanna-bes.