Maths is both a versatile, relatively straightforward and highly respected A-level for any course at uni. I think anyone, with the ability, is a fool not to take it.
I got a low A in maths gcse with very little revision. Is it worth doing it in a-level? Is it really hard?
I've got friends who got B at gcse and A* at ALevel. Anyway you definitely should, there's no other ALevel that opens so many careers and options to you