well do you want to study a liberal arts programme in the first couple of years, or go straight into econ+man? Do you want to study somewhere where you get relatively few lectures and then expect to read up and write an essay (paper) each week, but then have two or three hours a week 1 on 1 or 2 on 1 with a expert in the field, or would you rather have more lectures but limited office hours and more teaching done by TA grad students?
With an oxford degree, particularly E&M, you're not going to be at any disadvantage if you want to go into banking, particularly in London.