Unfortunately, I don't know that much about many of the newer, non-WotC settings, but they've already received a good amount of press already.
As for D&D settings, 2 of the "big" ones--Forgotten Realms & Dragonlance--both have similar advantages & disadvantages.
Advantages:
* Both worlds have a vast wealth of information on them, whether in sourcebooks, adventures, or novels.
* Both settings have a lot of name recognition, esp. w/ D&D players. The titles could easily gain player interest alone.
* Both settings have big-name characters that are very recognizable by fans.
Disadvantages:
* The vast wealth of information can be a hindrance, since an element that may have been "canon" has changed within a few years (via a new book or sourcebook).
* Just as these settings have their loyal fans, they also have their detractors. The names could easily drive away players as they attract them.
* Levels of knowledge amongst players & the DM. If the entire group is full of FR fans who've read every story & had access to every game supplement, then it may not be a problem. However, if there's a definite difference in knowledge levels (amongst players or players & the DM), then it may be an issue. (IMHO, this is a problem for a lot of games based off of licensed/popular properties, such as Star Wars, Star Trek, Lord of the Rings, Indiana Jones, Aliens, Marvel, etc.).
* As I mentioned before, the settings have big-name, easily recognizable characters. Which, unfortunately, some players may emulate too much, trying to make rough carbon copies of those characters with their PCs. Also, some players may want to have higher power-level PCs, in order to perform comparable tasks like their fictional idols.
And, OTOH, there's Oriental Adventures:
Advantages:
* Set in Rogukan, if you or your players are Lo5R fans.
* Gets away from the pseudo-European setting of D&D.
Disadvantages:
* Set in Rogukan, with AEG putting out their own source material for the game; may take a bit of work to remove the Rogukan elements in case you want to use it for another campaign (whether Kara-Tur, or a non-Japanese Asian setting).
IMHO, I'd say that you can't really go wrong with Greyhawk.
Advantages:
* It's the core setting, though there really isn't a plethora of setting-specific material for it, unlike FR & DL.
* You can easily use older material for more detail, if you want. And, there's multiple versions of its history, instead of 1 set "canon." (Whether you go with the Gord the Rogue/EGG development of it, the TSR development, etc.). It doesn't feel as "'canon'-heavy" as other settings like FR or DL.
* Current and future sourcebooks use basic Greyhawk setting elements. Easy to just drop in new characters, PrCs, magic items, & the like straight from the source material into a Greyhawk game.
* Has a fair amount of name recognition in its own right (esp. with old-school fans, and now new fans are allowed a taste via the Temple of Elemental Evil PC game).
* Homeworld of a lot of the "named" items & spells--Murlynd, Mordenkainen, Vecna, etc. Also home to a fair number of classic modules, as well (Drow, Giants, Temple of Elemental Evil, etc.).
* Has the perfect home base for adventurers--Greyhawk City. Full of its own intrigues, and possibly the best place to start or find an adventure.
* Comparitably less gods-intense as other settings like FR & DL. No Chosen of such-&-such deity; no cataclysmic world-changing battles every generation; etc. IIRC, Iuz is the only deity present in the Prime Material, but he seems to serve in more of a Sauron-like role than other deities.
Disadvantages:
* Since there is not 1 set "canon" history for it, things can be a bit confusing/messy for you if you want a set group of events.
* No real supplement development for the setting itself. Unless things change, there won't be any softback or hardback book supplements discussing the Pomarj, Vesve Forest, or Bandit Kingdoms. Much of the setting-based material is from older editions, which you may need to obtain via eBay, used book stores, etc.
* Not as big name-wise as FR, DL, or Rogukan.
IMHO, I think that Greyhawk would be your best bet (of the in-house, D&D settings). I think that though it has the basic information, you could really feel like you can make & change things in it easily, & (possibly) without any outcry from the players (which may not be the case with a FR or DL game).
Then again, this may be as easily said about other campaign settings, but here's one thing to ponder--with the D&D books, you've already got the basic stuff for the setting right there (maybe adding on the Greyhawk Gazetteer & Living Greyhawk sourcebook). No need to buy the core campaign setting book, the campaign setting monster book, various campaign setting regional books, a campaign setting deities book, etc.
JUst a bit of info to ponder. Hope it helps.