She spoke German, French and was taught Dutch a language she made the official language of the court during her regency.
Wilhelmina and Juliana had to be home schooled because they needed to be ready for duty at the age of 18 and both received good educations with plenty of attention to history, economics, defense, kolonial matters, international diplomacy etc.
Juliana did attend college for over a year to further her education but mainly because she really wanted to go.
Beatrix grew up working hard as she knew that a crownprincess cannot fail exams so she studied hard. She has always been a hard worker.
She is the only one who earned her college degree but that is more down to circumstance and the time she lived in. Im not sure if she is the most intelligent one of the four, her mother, grandmother and great grandmother were very smart women as well. Beatrix was by far the happiest one. She married for love and was never betrayed by her husband. She also had a lot more freedom than the three before her.