Two wonderful choices! Congratulations!
I think the earlier posters did a wonderful job of differentiating the two colleges.
Just one thought on Williams. Our family has been very impressed by the English department but not so much by the psychology department. Take a look at the course catalog and see if it reflects your interests and your beliefs about what psychology is all about. Our family found that the most satisfying psychology courses were not in the psych department, but rather in the English and History departments (such as those taught by the wonderful History Professor Kohut— and yes, he is the son of famous psychologist Heinz Kohut!).
Williams is a special place, though. The two students/one prof tutorials are wonderful, and a good symbol of the attention that students receive at Williams. Even non-tutorials are usually small discussion-oriented classes. You will get to know your classmates and professors very well, and your skills of thinking and writing will develop fantastically. And almost all classes are amazing— if you read the reviews of the professors and courses (accessible to current Williams students only) before registration, you can ensure that you have four great classes every semester.
If you go to Williams, try to broaden your social connections in the fall by taking advantage of opportunities to interact with your freshman entrymates and Ephventures companions as well as with your teammates.
Good luck. You will get a fantastic education at either school. It really comes down to whether you prefer large or small, urban or rural, fraternities or no fraternities. You can’t go wrong here- it is just a matter of personal “fit.”