My Least Favorite Setting: Eberron
It feels like they were trying too hard. Come up with an excuse for everything from every book to fit somewhere, and power it all up a notch. I loved what one of my friends once called it: "DnD X-treme!!" referring to PC golems, the "Extreme Explorer" prestige class *shudder*, trains, a fantasy version of Coruscant with demographics that make the city about as empty as farmland. Making magic so utterly banal that there is an NPC classes devoted to churning it out, and PC class that does it on an even larger scale, but even though it's that common don't expect to find any NPC's who can cast high level spells for you, by the time you're mid-level you're one of the highest level people in the world! To me it feels like it was designed from the ground-up to be a munchkin's personal, private playground where they get to have lots of neat stuff, be the highest level people in the world, use every trick from every book, beat up every monster in the MM, and "win" D&D.
My Favorite Setting: Forgotten Realms.
I don't use it as a showcase of Uber-NPC's, and I'm not a slave to any metaplot. My PC's hear about the metaplot in passing, as rumors or at best they catch a glimpse of it (I throw out references to metaplot events to remind PCs that they are not the only adventurers in the world). The only "named" NPC the PC's have met in my 7+ month campaign has been Princess Alusair of Cormyr, and that's only because the PC's are based out of Cormyr and decided themselves to go petition the Crown for something. Elminster and the gang have way too much to do to swoop down and save the butts of every adventurer who gets in over their head. He's an archmage, not Superman. At most, an Epic Realms campaign should probably have them at least appear occasionally, but it's a big world, and plenty of arm-room for PC's to adventure without bumping into famous NPC's (unless the DM wants them to).
The actual reason I like the Realms is the depth of the setting. I can point to any place on the map and it has not just a name, but a culture, a history, politics, famous locals, and plenty of adventure hooks. Also, all my players know the Realms very well, having played in it under many DM's for many years and in some cases having read many novels, so when I mention Zzass Tam, or the Church of Helm, or Zhentil Keep my PC's all know exactly what I'm talking about, the reputation of the organization/country/person, and it really gives the feeling of a "shared world" you just don't get in a homebrew or almost any other setting.