Vassar is laid back. It all depends on your major, your personality, etc. but most of the student body in general is cheerful and easygoing. From what I hear about Swarthmore, their academics are much more intense and they do much more work per class. But I don't think that there's cutthroat competition at either school. Anyway, the best way to tell whether you'll fit in is to visit Vassar's campus, check the amount of people studying in the library / partying, and see what it's like for yourself!