I found English really easy at GCSE, if somewhat boring. But it's the kind of subject that you either have to work really hard for or just be good at writing essays. i found it quite boring but we had a great teacher who worked miracles with us - I don't think anyone got less than a B, even the people who got Cs or less in all their other subjects!
I've got to say from that list I'd say Art was the 'hardest'. The work was easy but it was the sheer volume and time consuming work they expected that made it hard. I got away with doing it all at the last moment but it is a bit stressful when all your other teachers are wondering why you've not done their homework because you've been preparing for your 10 hour exam...
Not on the list was Greek. I did classical greek at GCSE (laugh away!) and I think that was the hardest GCSE because there was a ton of set text to learn, with all the translation, and then loads of vocab... we had a good teacher but i think i got a bit lucky with that one!