I haven't tried any conservative or libertarian groups yet.

Given that conservative (I believe especially evangelical groups) donate the most to charity, it's probably worthwhile checking them out.

My understanding is that their current approach to the inefficient charity problem involves organizing trips to the countries in question and having members personally help the charity. While this is clearly not the most efficient approach, it does help with the "most of the money winding up in the hands of middlemen" problem while also generating warm fuzzes.