This Year's Model of Humanity

I think it is easier to find good or at least passable H/D fic than anything else in HP fandom. It's my experience at any rate. And it's true that it probably is because there's such a huge quantity of it, that of course there are going to be more decent-written ones by default. But I also suspectt it is because the writers for it get a lot for free, seeing as there's plenty of canon interaction between the two of them (which isn't the case with many other enemy-ships.)