This is a review for both Maths A and Maths B together.
I initially signed up for Maths A, and I would encourage people not to be intimidated by other people signing up for Maths B; half of them drop down to A after a few weeks.
The A course has more or less the same topics as Maths B, but in less detail, and so goes at a slower pace (but the exam at the end of the year is the same, you just choose from fewer questions). If you’re not particularly confident, or just don’t enjoy maths very much, then this course probably suits you, it will prepare you well for almost any further maths you’ll be required to do. However, if you want to do theoretical physics or the like, you’d probably be better off doing Maths B.