I started DMing during the setting boom of 2nd Edition, so I still really like a lot of those settings. Planescape, Spelljammer, Ravenloft, Dark Sun, and Birthright are ones I really dug, with Planescape, Dark Sun, and Birthright getting actual play. Of those, I enjoyed playing in Planescape most, but still harbor secret hopes of running a Spelljammer-inspired game.
Since then, I've run Eberron (although not with D&D rules) and a lot of Golarion. I don't foresee running anything but Golarion for the next couple years, honestly, but I'd still snap at the chance to run Planescape, Spelljammer, or Birthright.
Cheers!
Kinak