well it mentally I think सिंडरेला because after her father died she was bullied, but still believed in hope and had faith things would get better. I think that makes mentally powerful. Physically I think Elsa is most powerful because she has magic and can make people fear her and प्यार her. But honestly I think all the royals have their own power within and that makes them all powerful.
Physically speaking....... Elsa. Her powers could cause destruction. However, Rapunzel's power is Resurrection. आप could be dying and she could decide whether या not to save you. Ariel can communicate with जानवर though! and Pocahontas can paint with all the रंग of the wind! ;p
