English language was my worst so I'd be compelled to say that, French was my second worse, and I kinda considered it harder, so French was too, I'd say. Didn't really revise for them though (just hoped I was smart/lucky enough to get Bs in them, which it turned out I was).
Art however was a hell of a lot of work, even at GCSE it was remarkably high workload compared to any other subject (although obviously it wasn't mentally straining or remembering stuff like most other subjects, which makes up for it).