i am doing edexcel maths
edexcel c1 and c2 are not hard
i finished m1 s1 fp1 c1 c2 and currently finishing s2 but personally i don't think they are hard, but i am not sure about other exam boards,
i am not sure how easy or difficult the other modules would be (i.e. m3-m5, fp3, S3-s4 )
i would recomment edexcel because the are lot of resources, so you can revise for the exam properly