Greyhawk.
Regarding Advanced Dungeons and Dragons 1e, the official setting is the one that the DM invents. Homebrew. Everything else is suggestions and inspiration − and a mess that requires homebrew to make sense of.
Greyhawk is something else. Greyhawk is an intellectual challenge to see if it is possible to use every suggestion that TSR ever published, and fit it into a single setting − somehow, somewhere. The end result is a mixed success. But interesting. It also defines an era, maybe sorta like a cd of the musical hits across a particular decade.
I think you can ‘sell’ Greyhawk as old-school D&D, so that new players can get a sense of the origins of the D&D game. How it all started.
On the one hand, Greyhawk is less my setting of choice. There were ‘suggestions’ during the TSR era that I prefer to ignore.
On the other hand, there is a mood of ‘anything goes’. Players can build almost any kind character concept − and it *will* fit somehow somewhere. So players have alot of latitude.
So. If I am a player, I am cool with Greyhawk. Because I know if there is some customization that is important for the character concept, it will probably work out well in the context of Greyhawk.
This abundance of player empowerment (!) makes Greyhawk an appealing setting.