They're both very accurate. They will both be off a bit at times, but they're both more accurate than the NPD I would believe.
Either one you go with is completely fine, as they're almost always within 10% of each other on weeklies and 5% on LTs.
If you're going to write an article, stick to the numbers that sound more credible (ie, don't use the leaked numbers from MC, use the official from Enterbain, or vise versa, but I guess that is obvious)
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS