Well it's going to be rather different for different people, who will often have different skills and strengths. For me, A Level maths would probably be quite the nightmare, so perhaps I'd say that. But it's not in the poll; interesting...
I'm sure most people would find further maths very challenging, but for me its not too bad. I would find something like english lang/lit very hard though. It's a bit of a silly poll.
Statistically, at my school anyway, Chemistry is far and away the hardest subject at A-Level, followed by English lit and then German I think. I voted Chem. in the poll.
Im glad people agree with me on chemistry lol, i find it awful, and i do quite a few subjects so i have a wide range and i still say chemistry is the worst.