Seeing the culture of StackOverflow, I would choose to be dead in the ground rather than ask a question there, even a question that can't be easily answered elsewhere. Volunteer-run sites need a mix of enthusiasts who do the real work of the site and janitors who keep things from being too chaotic, but enthusiasm dims while the desire to impose order never does, so eventually the janitors take over.

MathOverflow has a much better culture, so I ask (and answer) questions there. I'm not quite sure why it's worked out better there, though I suppose it's something to do with the population.