I disagree with people saying that Maths and Sciences alone are the most respected. If you do Maths and Science A levels, by themselves, you're showing that you can excel in one area of academic study, which is all very well, especially if you want to do something such as Medicine or Engineering. However, it is pretty much a narrow area, you aren't really taught in these subjects how to think critically and construct essays. I think an ideal applicant in general would have a mix between critical, written subjects as well as scientific/maths subjects, but of course it all depends on what degree you are aiming for.