I think Art or further maths. In general you need to have some sort of talent in order to do well in them.
Whilst I think I have more of a natural talent for Art than say maths, the reason why I didn't pick Art was purely because of how difficult the workload would be for me. I am quite the perfectionist when it comes to drawing or painting.
I will spend literally the entire day making sure a piece is perfect like in Art GCSE.
I'd rather have 6 maths exams than pick Art for a level.
Getting an A* in further maths is hard if you don't have some sort of mathematical ability, and getting an A* in Art is just as bad if you can't draw. They are both just as bad as each other, it all depends on the person.