Ugh. This question is just way too common.
There is no hardest subject. There is no easiest subject. It is all subjective. If you are good at essays, but bad with numbers, you would probably find Further Maths to be extremely difficult, but could find History to be a breeze. The opposite could be true for someone else.
Different people have their strengths, so it's very difficult to compare the different subjects on something so subjective as difficulty.