My advice would be to do some basic background research into what a particular uni will offer you both in terms of your progress within the course and afterwards. Find out if their vision is your vision, and what the outside world thinks of their students. - I know Yale has a reputation for some things, but you have to be happy there too, three years is a long time to be wishing you had chosen somewhere else. Check how well the supervisors are respected, check on their work and see if you could work with them remember that they need you too!