> My dream is to one day create my own startup (possibly right out of college)

If you're going to start your own right out of college, the most important thing will be having people to do it with you. You'll get great work experience at either company. Go to the one where you think you'll be able to make more, stronger connections with other interns. Leave your internship with a list of potential cofounders. I'd probably choose Facebook based on the number of interns, unless you think that culturally you'll bond more with the people that Palantir attracts.