6. Princeton University
Princeton is an old college which was founded in 1746 and it is one of the oldest colleges in the USA. It is best known for having a number of smaller programs with not as many students as other elite colleges.
This college does not have a medical school, law school, business school, but instead it has evolved into a humongous thin tank which is research driven. It tends to continuously to challenge its students with a highly difficult grading scale
Even many of brilliant minds who come to Princeton from all around the globe find it difficult and need to study much harder.