Settings
1) Greyhawk. It's just awesome.
2) Ravenloft or Dragonlance. They tie because they're both so well designed as both games and mediums of storytelling.
Eberron has officially taken the place of Forgotten Realms as the campaign setting that sucks the most in my opinion. Sure, there are some cool things about it (I like the fact that high-level characters are rare), but otherwise it's just too generic, too much like a MMORPG (an entire continent that's basically one big dungeon?), and too zany for me to consider running a serious campaign there. I might play a warforged rogue that works for the Khorvaire Express Delivery Company based out of New New Sharn if someone wants to buy us a big green airship, but otherwise I'm not interested.
I don't generally like the Realms because of the logical incongruities. See Power of Faerun for example, where a CR 40 dragon is just chilling out in the mountains. Or the experience I've had where most every FR game I've ever seen has either Drizzt or Elminster or maybe Storm Silverhand as an NPC with the party just because the DM wants to play them. FR has some good material in the older product line, such as RUins of Undermountain or Throne of Bloodstone. Is it just me, or has FR gotten even more Tolkienesque since a certain movie premiered in December 2001? Hmmm...