Single maths? Just C1/2/3/4 M1/2 or S1/2 or D1/2 ?
Easy. C1/2 are a cakewalk. So are M1/S1/D1. If you ace these then getting an A overall is easy.
The content of single maths is really not difficult. Its like 60% calculus with some trig seasoning. If you just do all the past papers and a million questions you can do very well quite easily. The core modules are very repetitive and formulaic - you can easily train yourself to do them even if you lack a mathematical talent.
I would say, of the applied modules S1/2 are the easiest imo. D1/2 are soul crushingly boring and M2 is all over the place. If youve got the engineering bug then mechanics is the obvious choice and i know people who could get 95+% on every M2 and M3 paper easily. However, S1 and S2 are just a matter of learning the distributions and the copy+paste responses. Dont take D1 and D2. Everyone will say "Oh, decision maths is the easiest" and yeah, it probably is but bubble sort is worse than grating my own nose off.
If you get 90% in C1, C2 and 2 applied modules then you only need 60% on C3 and C4 to get an A overall which is easy. If you want the A* then just do past papers constantly.
Oh, i did OCR maths and idk if every exam board has this modular structure so i could have just spoken a load of nonsense but basically only the last 20% of single maths is particularly challenging.