[otachack]

Why not both? If you can afford it, of course.

[kqr]

That could make sense if both are equally good, or if it's down to personal preference and one has to try both.

But GGP made the argument out to be altruistic, that paying for one over the other is because it's better for the world. If that is the motivation, I would want to donate however much I could afford to the one with highest impact!