Hi There
Perhaps I may be of assistance here. I have a MPA (Masters in Public Administration) from Columbia University with a concentration in international economic policy. In my opinion, if your goal is to work somewhere like the UN where it is highly development-focused, you would do well to target a top MPA school. These schools offer networks and connections to UN, World Bank, IMF, etc.
However, it kind of depends on what you want to do at these organizations. If it is policy or development related, you definitely should go for a MPA instead of a MBA (in my opinion). However, if it has to do with some finance or business functions within these organizations, then a MBA or a MPA may both work (in some cases, maybe even a MBA would be better).
hope this helps!

If you decide to go the MPA or masters of international affairs route, please feel free to private message me, as I know the rival programs to Columbia fairly well.