I really enjoy homebrew a lot some of the best games I have played in have been homebrews.
My favorite published gameworld is Kingdom Of Kalamar. I like the real feel feel of the world the fact that there are different languages. I like that there are a good choice of Gods but not different pantheons based on race. I like the sticky moral dilema's like legal slavery.
other gamesworlds I really like are:
Scarred Lands
Dragonlance
Freeport Modules
Old Runequest
Greyhawk
Forgotten Realms AD&D better than 3.0
Before two days ago when I got the Eberron book, I'd have said Greyhawk, but I suspect that if I had ever played or run Planescape it would have won hands down for me.
It has been Scarred Lands for a while now, although a recently picked up the Midnight campaign setting and I think it might end up my favorite, with SL right behind. I have not finished reading yet, and I have not actually tried a Midnight game yet, so its hard to say.
This was a tough call. I voted for the Realms but I'm also a huge Greyhawk and Kalamar fan. I like Spelljammer and Dragonlance as well. I voted for the Realms cause I'm a big fan of the material for 2e that has really fleshed out the setting like the Volo's Guides. Greyhawk was a very close second, I like what Erik Mona is doing for the setting and Carl Sargents stuff for 2e like Ivid that helped build and expand the setting.
Not having a lot of Kalamar stuff but the main books and a few others, isn't a drawback as I see my vote but Kalamar is up there as well. The setting really adds a different take and feel to "traditional settings" I really like the Orc and Hobgoblin books and the Geanavue city book and I'm looking forward to future books by the writer Wiggy.
I voted for Greyhawk because the world is still so intriguing before the whole Out of the Ashes thing. It is the world I started in and we still campaign in. I mention Scarred Lands because I just discovered this not to long ago and it is so very different and has tons of potential that I will be running a campaign in this world in not the too distant future. You should seriously check it out.
Honorable Mention: Judges Guild's Wilderlands Setting, especially the invenerable City State of the Invincible Overlord.
Forgotten Realms is fun in its own way. And Eberron shows a lot of promise though I haven't been able to play it yet. But by far and away my favorite setting is DragonLance. But that just might be because I like the books so much.
Planescape is still #1 with me, but Eberron has quickly bolted to a solid 2nd place.
I have a love/hate relationship with Dragonlance. Taladas easily ranks within my top 5 favorite campaign settings, while Ansalon has to duke it out with Forgotten Realms for dead last.