Favorite RPG Setting
If you have read my previous answers, it should come as no surprise that my favorite setting is Star Wars. I am not going to go on about it again here, I have run two campaigns to completion in this setting and loved both of them. I can actually be more specific because both of those campaigns were set in the Elrood Sector, the subject of one of WEG's Galaxy Guides.
The great thing about the Elrood Sector is the level of detail at which it is described, each planet gets a few pages, some hooks, and a few characters. There is enough there to build a campaign around, but not enough there that it becomes cumbersome to remember it. In fact, while both my campaigns were set in the Elrood Sector, they were two very different versions of the sector.
I should mention two other settings in which I have run a lot of game sessions, Stonehell and The City State of the Invincible Overlord. I don't think it is a mistake that these are both very limited settings, one is a city, and the other is a dungeon. They are both kind of the opposite of the Elrood Sector, they are limited in scope but described at a high level of detail.