Congratulations on your acceptances! With funding out as a factor I would consider curriculum, brand (bleh, but it matters, right?) and location:
Curriculum: Which program has the core and classes that you really want? I know that Sanford has a strong core, while maintaining the flexibility to tailor your MPP with a selection of electives from across Duke's graduate schools (law, Fuqua, etc). While you can choose a specialization you don't have to, and outside the core you can pretty much design your program based on whatever classes you want to take. I didn't apply to WWS so I am not entirely sure what their curriculum looks like, but I have heard that it has a pretty specific core, specialization and advancement requirements.
Brand: Duke and Princeton are both amazing, but I believe (other commenters, feel free to correct me!) that WWS has an edge over Sanford, especially in international policy circles, and is considered on par with HKS (that Ivy thing...).
Location: Where do you want to live??
Good luck! And hey - if you choose Duke, I'll see you at Sanford!