My favourite published campaign setting would be...

[1auxy]

I've been running my 3.5 games in the Wilderlands of High Fantasy for about 3 years now and absolutely love it.

 

[Serendipity]

1. the OTU (Official Traveller Universe) - from milieu 0 to TNE:1248. I love the pants off it.
2. Gygaxian greyhawk - not so much the Greyhawk Wars + stuff.
3. Glorantha (preferably in it's RQ expression - go Uz!)
4. Spelljammer
5. Planescape
6. Eberron
With very strong runners up in the form of the Known World/Mystara, Midnight, Fading Suns, Kult, Unknown Armies, the old World (fr. Warhammer), and 2300AD.

That's a lot - which is funny as I generally homebrew.

 

[GrumpyOldMan]

1) HârnWorld, for not-quite medieval goodness, magnificent maps, and staggering detail.
2) Glorantha, for outright strangeness, my runes are death, truth, and death.
3) Arthurian Britain, for the glory and tragedy of knighthood.
4) 1920’s New England, because I’ve lost my sanity.
5) The world of Earthdawn, because of an elven archer and a gay wizard.

 

[lmpjr007]

The 13,000 comic books suggest that DC is my favorite published setting.

I guess my would be a split of Marvel and DC. Thank god for the Marvel Super Hero RPG! LOL!!!