Maths is definitely a really useful thing to have as there is a large unit in the course that is pretty much purely maths, it is also good that you are confident re-arranging and putting things in standard form because these feature heavily in all areas. However don't go into physics relying solely on the fact that you are good at maths, in some of the areas, in particular quantum physics and waves you also have to understand the concepts and be able to explain what's going on, people associate maths with physics and often overlook this aspect, which is often the most challenging part. When making your choice I would bear the written aspect in mind and perhaps look at a past paper or two and see if this is something you are happy to do.