I know children's cancer and other horrible things pull on more heart strings, but Wikipedia makes such a huge wealth of great information available to such a huge percentage of the world, including many poor people who might otherwise not have access to much education. Saving sick kids is kind, but there are lot of healthy kids who could use a leg up too.
I honestly don't value the other Wikimedia projects very much, and I'm sure there is waste in their policies and beuracracy, but assuming Wikipedia is only getting 10% of my donations, I still think it's great bang for the buck.
If there is a better charity, I'd like to know about it. However, this article reads to me as "Meh, you shouldn't really feel obligated", and I don't think it said much that was useful.