This is definitely a huge problem, especially with socially-competitive charities. Things like breast cancer awareness and helping the local needy around Christmas are so popular that they're locked into ugly advertising struggles. And if people don't do their homework, the most efficient fundraiser will be the charity that spends no money on the cause (or just enough to stay exempt).

This seems like a good time to plug Givewelll. Their entire goal is quantifying the good done by charities and promoting the most efficient. They compare globally, but even if you want to give to something specific like animal welfare or local homelessness, they have some good efficiency tips.

http://www.givewell.org/