Some real subject elitism here. Universities do not think highly of one subject over another. They do, however, produce a list of 'facilitating subjects', which are subjects that universities require students to have to get on to many degree courses. For example, lots of science degrees require students to have two or sometimes three A-levels from Maths, Physics, Chemistry or Biology.
The list includes: English Literature, Maths, Further Maths, History, Classical/Modern Languages, Physics, Biology, Chemistry and Geography.
If you know what you want to study- English, for example- and you know that most universities specify that they want English Literature at A level in order to study it, your others two choices are open. However, if you don't know what you want to study, I highly recommend picking any three of the above so all pathways are open for you.
In a way, I think choosing one AS from every department- Physics, English Literature, History and a Language- shows how versatile you are, and would look better than three sciences. But this all depends on what you want to do!
Best of luck