A-level subject choices

Why are you taking 4 at all? Does your school require it?

Universities do not award "bonus points" for taking extra A-levels beyond the required 3 (except Cardiff medicine for achieved A-level grades, I think). In fact most universities up to and including Oxbridge have clearly stated they much prefer a very strong set of 3 A-level grades to a more mediocre set of 4. A*A*A >>> A*ABB as far as unis are concerned.

If your school requires you take 4 then just pick whatever and drop it ASAP.

We can pick 3/4 levels but I'm not sure if I want to do law or pharmacy so I want to take a range ish and just go from there and drop what I won't do well in (or what i enjoy least) before Christmas-ish.

Law has no subject requirements and readily accept applicants with all STEM subjects. Just take your original combination. That said, pharmacy does not require A-level Maths to my knowledge at any uni so you could just as well swap that for an essay based subject if you wished. Either way, you are covered in both directions just doing 3 A-levels