When I applied to Oxford I was interviewed at several different colleges. Although I spent only about half an hour in the college, Mansfield stood out as being the friendliest: all the colleges had set interesting questions to discuss, but it was the Mansfield tutors that seemed the most genuinely interested in my response.
Since Mansfield is one of the smallest colleges in the university, both in terms of the actual college site and the number of students, it didn't take long at all to get to know people and to feel comfortable and relaxed. This, as well as the close contact with the tutors, made managing the transition from school to university much less stressful.
I was fairly late in choosing my course of study. I was torn between what I saw as more pragmatic and career-focused options and the subjects I genuinely wished to pursue out of sheer interest. Now that I see the options open to maths students and graduates I'm very pleased with my decision.
The diversity of the material covered in the lecture courses in the first year alone is incredible, but there is still enough overlap to see how the different areas interact. For example the application of theorems from analysis to prove results in calculus, and then the further application of this to derive results in dynamics.