I use them all, plus a large number of other prime material worlds that have been named in the source material (Ortho, Threnody, etc). I've used FR quite heavily, more so than any other specific world on the prime. I had three PCs from Toril last campaign, and one PC from there in my current game. I've had some plot arcs across Faerun everywhere from Calimshan, Iron Fang Keep, the Lake of Steam, the High Forest, and the current plot arc in my 2nd Storyhour takes place in the Great Dale. I adore FR and so it sees heavy use even in a planar campaign, and I see no reason to hamstring my players' enjoyment by switching to a cosmology that I see as floating somewhere south of awkward and lame (my players have an even dimmer view of the retroactive cosmology shift than I do, both in substance and in implimentation. If I ever tried to use it, the words 'railing kill' might be invoked).
I've used lots of stuff from Grayhawk, but never the world itself as a destination. But that's largely from my own unfamiliarity with some of the 1e/2e material (though Mona has succeeded in getting me interested in learning more).
That said, while Krynn is still out there, they tended to unfortunately come off as planar retards pre-3e (because the novels tended to ignore the fact that they were in a shared world, and the planar source material seemed to return the antipathy by presenting them as a backwater). I can't say that I've ever used Krynn itself, though I've used a few NPCs from there from time to time.
I've only used Athas (and Dregoth...) once, but largely because it was already so difficult to get out of that using it much presents logistical issues on getting the PCs back out of the place.
And of course, Ravenloft is still out there drifting in the depths of the ethereal. Woe be to anyone intentionally looking for it.