The Most High-Magic Setting of D&D?

[Libertad]

If we go by official campaign settings (both TSR and WotC), which one would you say has the most magic in terms of common accessibility, number of spellcasters in the population, and overall supernatural wonder (floating cities, extraplanar beings traveling about in capitals, etc)?

I'd say it's tied between the settings of Eberron and Planescape. Eberron is undergoing the magical equivalent of the industrial revolution, and the Dragonmarked Houses' inventions replicate advanced technological devices; lightning rails, everyone?

Planescape is tied due to its exotic extraplanar environs, especially the City of Sigil. Angels, genies, and demons are common inhabitants and travelers instead of nigh-mythical beings, and the supernatural suffuses entire planes.

[Sith_Happens]

Don't forget Spelljammer.

[ghost_warlock]

Pre-4e Forgotten Realms. You couldn't take a crap without 15 deities getting involved and Elminster scrying on you.

[Ravens_cry]

Don't forget Spelljammer.

No, one certainly can not. There is certain parallels in Planescape and Spelljammer in that both can be meta-settings that have means to explore others.

[Arcanist]

Pre-4e Forgotten Realms. You couldn't take a crap without 15 deities getting involved and Elminster scrying on you.

I was about to say "How come nobody has mentioned FR?" But yeah; Abier-Toril has, if memory serves:

• Floating Cities (Ask the Netherese how that turned out btw, not a good door opener)
• at least 3 Planar beings in any village (Seriously, I'm starting to think they'res more God's then Worshipers...)
• Easily accessed Planar Travel (Moving an entire city through the plane of shadows? HELLZ YEAH~)
• Most Spellcasters (They have like 3 Magocracies...)
• Most amazing magical items (WHAT IS A: MYTHALLAR! Seriously, I think House Cannith would have had a hell of a week with one of those...)

Honestly, I'm hoping WoTC makes FR more like the Tippyverse (Less raw, more tele circles to everywhere and back). Hell in 2nd ed the Netherese could actually go through Crystal Spheres and back (which allowed for some interesting high magic adventures)

On a side note: throwing Sigil out there is just plain unfair

[Eldan]

Forgotten Realms has probably the largest density of powerful mages. However, it still has, according to the books, a more or less normal population of non-magical peasants who enjoy few magical benefits. Eberron doesn't. And since the OP asked for most accessible magic, definitely Eberron.

Planescape has powerful mages as well, but, again: the magic is not very accessible. Many mages hoard it. Your average hive dweller won't ever use all that many magical items. And the planes themselves are certainly magical, but that doesn't mean your average mage will be able to use that power without having it backfire.

[Yora]

Planescape is highly magical, but most of that magic is just there as part of the very strange environment. There isn't actually that much useable magic that can be used on purpose.
In Sigil there are all those portals to everywhere, but these portals are just there. Nobody builds them, nobody can control them. And there's lots of magical creatures, but in AD&D, I think most of them where not able to use them for anything else but to throw fireballs and the like.

[Tengu_temp]

Forgotten Realms has probably the largest density of powerful mages. However, it still has, according to the books, a more or less normal population of non-magical peasants who enjoy few magical benefits. Eberron doesn't. And since the OP asked for most accessible magic, definitely Eberron.

That's because Eberron was written by someone who thought about how fairly common access to magic can affect society, and Forgotten Realms weren't.

[Hiro Protagonest]

If Eberron is the Industrial Revolution of magic, Forgotten Realms is a world where there are brilliant godlike engineers who tightly clutch their inventions and say "mine!" and leave everyone else in the Medieval Era.

And then they give some of their weaker inventions to guys who clear out orc tribes and ogre dens, as if the adventurers are contestants on a game show.

[Eldan]

All true, but Eberron still has more widely disseminated magic. Which is what the OP asked for.