Stephanie:
To many children, Disney revolves around Pixar characters like Woody and Buzz Lightyear instead of Mickey Mouse. If your girls grew up with Playhouse Disney and modern Disney movies,
Hollywood Studios may be fun to explore. Make sure that you see
Beauty & the Beast early in the day before crowds and lines grow, and measure the girls' heights to see if they'll be able to ride Rock 'n' Roller Coaster in order to manage expectations.
If your girls love animals, then a visit to Animal Kingdom should be considered. The gorilla trails are a must-do as well as the Flights of Wonder show. With both
Expedition Everest and
Primeval Whirl, they can check roller coasters off their list, but you'll need to make sure that they meet the height requirements (44" for EE and 48" for PW). If they don't meet the height requirements, I would go to DHS because at least they'll have princesses there with the Little Mermaid and Beauty & the Beast.
Keep in mind that regardless of your choice, your daughters--and you--will love either park. They are simply different.
Wishing y'all a magical vacation!
Whitney