In theory? I'd say Planescape or Spelljammer. Both settings are just full of "wow" factor. They can be as gritty or as high fantasy as you want, literally anything goes. You can focus on action in a bar in Sigil or on the Rock of Bral, doing dirty work for various factions, and dealing with low intrigue in back alleys.
Or you can focus on sailing the Astral Sea aboard a ship made from the head of a long-dead Goddess that no one even remembers, fighting Githyanki along side a crew of planar misfits, under the command of a Marilith Pirate Queen!
Or you can focus on exploring strange new worlds, seeking out new life and new civilizations, boldly going where no human has gone before, aboard a Gnomish Dreadnaught crewed by British Hippo-Men armed with muskets and a love for things that go BANG!
In practice, Eberron is the ultimate kitchen sink setting. However, unlike other settings, it takes the existence of fantasy elements and runs with it. Magically empowered merchant guilds engage in Machiavellian politics while the world recovers from an all-out war fought with undead, monsters, and sentient robots- robots who now are trying to find a purpose in a time of peace.
The minions of dark gods and aberrations from BEYOND lurk in the sewers, the monsters are trying to rebuild an empire, the touch of Dragons can be seen everywhere, Elves worship their undying elders, there's an entire continent of ancient Giant ruins infested by scorpion-loving dark elves, Halflings ride velociraptors on the Talenta Plains...
There's just no end to the stuff available. Sadly, however, I feel Eberron, since it was created for 3e, hasn't been the same in newer editions. The options available to players have been far more conservative, and this is a setting where it's perfectly ok for your Halfling Fighter to suddenly use the strange powers of the Mark of Hospitality to conjure an extradimensional luxury hotel for the party in the middle of nowhere!