A piece of advice that I would give; a lot of people at my College have chosen Maths, Physics, Chemistry and Biology because they think they will get into a better university by doing that.
If you are most interested in those four subjects, and you are capable of getting good grades in them, then go for it. However don't go for them thinking that because you got a few A*'s at GCSE you are pretty much guarenteed an Oxbridge place by choosing those subjects, they are difficult and not to everybodies tastes.
A "B" in Chemistry doesn't trump an "A" in English Literature. A "C" in Biology doesn't trump a "B" in Economics etc... unless you are looking at specific courses. Obviously there are some subjects regarded lower than others, such as General Studies, Media etc... however generally most A Levels are on par until you look at a specific course.
If you don't know what you want to do for Uni, go for a mix of subjects that you are good at and enjoy, whilst thinking of what kind of options they could open for you further along the road.