There have been a fair few articles on LessWrong about utilitarian giving, with existential risk reduction and foreign aid being the most commonly recommended. Given that for many LessWrongers maximizing utilions is a major T. In my own investigations, I've found terribly few well-researched critiques on aid. Most of the criticism that does exist focuses on aid given directly to governments. Whilst this does make up a large portion of overall aid given, this is mostly irrelevant for e.g. deciding whether to give to any GiveWell recommended charities.

The major problem with writing such an article would be the lack of high-quality, academic research in this area. Having said that, there has been [i]some[/i] good research, and doing some original research is not out of the question.

Full disclosure: If you did choose this as a topic for a future prize, it is very likely that I would submit an entry for it.