Y will be an easier and better fit - academically, socially and culturally (for US kids)
The one advantage of the UK system is that you will graduate in 3 years.
But you can quite easily do this at Y as well. Buy why the rush? I would spend full 4 years to have the best time of life.
Y is a lot more flexible in customizing an education for you.
So the answer is actually quite clear, if not a no-brainer.
