I love Greyhawk, of course, and have a vast GH collection and (at the risk of being immodest) knowledge, but even then, I’ve done homebrew way more often than Greyhawk. My current campaign, the world of Erseta, is a homebrew campaign.
On the other hand, I was quite a fan of the Forgotten Realms up until a year or two after the gray box was released; after that, it just got overwhelming (but never actually played in or ran it). We played several campaigns (and I DMed one) in high school that took place in the Wilderlands (back when Judges Guild was still putting out new stuff). We had a terrific Dark Sun campaign while I was in the Air Force (I played a half-giant). And I took a stab at Ravenloft, but mostly looted it for ideas (and monsters– “if you try to conjure an earth elemental in a graveyard, you’ll get a grave elemental”) that I ported over to whatever campaign I was doing at the time. Other than that, I’ve never done Forgotten Realms, Mystara, or Birthright, or Dragonlance, or Kalamar, or any of the others.
I’m curious about something related to this. How many others have relied more on homebrew than published campaigns? (And if so, what rules did you use with it?) I ask because I get the sense that the homebrew campaign is a dying art, and more modern players rely heavily on pre-published settings and adventures.