Excluded: Forgotten Realms
Runner Up: Many depending on my mood that week: Ptolus, Freeport, and Planescape.
After that its a close run between Birthright, Greyhawk, Dark Sun, Ravenloft, or Wilderlands. Eberron is still up in the air for me, some days I like it, some days I think it is too over the top.
I am currently preparing to run the new Pathfinder Chronicles adventures from Paizo, and the world looks good so far. If the setting continues to impress me down the road, it will become a contender for first place in my book.