None of the above, oddly. For me, the generation of a campaign world for every campaign makes it a homebrew.
Then I suggest ToEE, for sure. There are enough holes in the plot and setting to make your improvisational muse sing.Homebrew purist, definitely.
I've never even tried to run a published setting. I probably should, at some point, just to give it a try. But I love having control of the world and having the demographics and "feel" of the world in my head.
Most of my GM style is improvisational, too, and I think that would be much, much harder (for me) with a published setting.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.