Basically, your decision is going to boil down to want you want to get out of the master's program.
GU's MPP is a quantitative analysis driven approach to policy that addresses aspects of international development in a similar fashion to how local policies would be formed and implemented. It is not an international relations program and does really focus on diplomacy or state-based foreign relations organizations. In both you'll get some economics, although SAIS has more in international trade and macroeconomics. GU offers courses in macro, but it is not part of the core curriculum. Georgetown does have the School of Foreign Service with which MPP students can take courses, although it is sometimes difficult to get into the better ones (they have their Madeline Albright, we have our EJ Dionne/Paul Begala).
As far as post-graduation situation, I have friends from GU that now work for the World Bank, USAID, and several private not-for-profit groups. You'll be well positioned to work for NGOs at either school. If you are more interested in finance development vis-a-vis IMF work, probably SAIS would be better, likewise if you wanted to do development work through the State Department/Foreign Service, SAIS may be the better option.