Where do your interests/strengths lie, and what are any courses you are interested in? That would definitely help make the decision easier. From your subjects I can assume you are leaning more towards the maths/science side, so the question is do you want maybe a break from those subjects? Personally having a nice balance between my subjects has worked out really well since I can always switch between subjects, and get a break from one and not feel all the material is getting quite tedious. I would only be able to speak for the subjects I have done without 1/2, which are Geography, Psychology and Revolutions, which I can affirm were all great to get stuck into without having done the 1/2. What are you drawn to at the moment? It's quite difficult to recommend one since it is very subjective.