Which is more reliable? npd or vgchartz?

[Khuutra]

.....Listen

In terms of hardware sales, "reliability" goes kind of like this:

Nintendo's company (I forget the name) > NPD > VGChartz

This is to be expected, though. NPD's sample size is orders of magnitude larger than that of VGChartz, which has to extrapolate to a much greater degree. This isn't knocking ioi, either: what he does with his resources is pretty amazing. But this question is almost meaningless.