Keef's spot on. The truth is that for most jobs the choice of subject doesn't matter much. Qualifications are most often used as a filter to cut down the number of applications, and apart from some technical fields they are used for nothing else. You need to get past the 2 good A-levels / 2:1 degree barrier, if it exists, because if you don't have that then your CV goes in the bin regardless of what else you have done. Best way to do this is to do subject that you enjoy - very few people excel in subjects they hate.
However, once you are past that then you'll find that your subjects or grades no longer matter much. Just as Keef says, the biggest single decision factor in deciding who gets an offer is "Have they done anything significant, meaningful, or to indicate initiative and leadership skills?". That's what you are being judged against, so make sure you've got something here that stands out.