I think whether or not a subject is hard is subjective. What I may find difficult, someone else may be able to fly through it. If you're picking your A Level subjects can I please stress NOT to pick something based on its level of difficulty. If you pick something that you've been convinced is easy and it turns out being something you're not at all interested in, you'll be stuck doing 2 years of work that will make you unhappy and there's nothing more stressful than doing a course that you aren't interested in.
Explore what interests you and what subjects are targeted towards your preferred future career. I'm only in my second year of A Level so I'm not all that qualified to even say which topics are the most difficult but I've chosen subjects that were the "easiest" and lacking complete interest made me unhappy, stressed, unmotivated and it impacted my other subjects causing me to drop it.
I read an article not too long ago that said the 5 hardest A Levels were: Chemistry, History, Physics, Maths, Biology. In that order.
I have a mind for the humanities subjects and I find ENglsih lit waay harder than history. I don''t there is much to pick between the two subjects to be honest though.