Transportation is much better at Poly- Poly is walking distance to TTC, so getting to epcot is easy. GF isn't bad, but you have to take the monorail to the TTC which could be packed since it is a later stop than Poly and the Contemporary.
Rooms - don't get me wrong here, both are amazing. I feel that the Poly has a better theme, so I say Poly.
I believe this is mostly about personal preferences.
I'm around your daughter's age, but I think that this depends on her and your family's interests.