I'm currently studying Maths, Further Maths, Biology (AQA), Chemistry, Physics (Edexcel).
I want to study Mathematics at University and I don't know which subject I should drop.
I am either going to drop biology or physics. I'm almost certain I will have got a higher grade in Biology than in Physics. However, I find physics much more interesting and it is more relevant to what I want to do at university. So should I drop a subject I enjoy more, or one that I am better at. Also, I have looked at the A2 specifications, and physics looks like topics that would interest me, whereas biology has one unit (AQA Biol4) which we have already done about half of, and is really boring, but the next unit looks really interesting. I also have the option of doing all 5 A levels to A2, but I don't know if that is worth it.
I took both Biology and Physics myself (just finished my A2 exams - Edexcel board for both). There is a HUGE jump in terms of both the amount and depth of content in Biology from AS to A2. In some aspects it's quite overwhelming actually. Whereas for Physics at A2 the topics actually became more interesting than AS and had less of a jump from AS to A2.
My advice would be to study the subject that interests you more. This will give you more motivation to study and do well. Besides, if you're doing 4 A2 subjects you're going to need a whole lot of motivation!
Edit: Also continuing with Physics really will help with your Maths, the more practise the better! If you think about it, keeping up with the maths in Physics could indirectly help you in both Maths and Further Maths. And Maths courses at uni will think more highly of Physics.
In general, universities only look at your top 3 A2 grades anyway, so it wouldn't matter if Physics is worse than Biology unless you're not confident with one of the other three.
I'd say drop the one you like the least.
Id drop Biology. Its the least relevant to your future degree, and you dont like it. Do what you enjoy - ultimately, thats more important than just 1-2 grades - besides, those A-levels are absolutely rock solid and will take you far in life, assuming you get decent enough grades. Oh and the fact you will be doing 4 anyway - you will do v well, Im sure