I already did my A levels here is my list.
1) Maths - Don't understand why everyone thinks it's easier than science it really isn't. Science is just common sense observations. Where is the common sense in C4 integration????? That proof for the sum of the arithmetic series was just pure Greek to me. What I mean is with science, even the hardest questions because it's all happening in the universe which always follows certain basic laws you can always apply those basic laws to get a crude idea of what must be going on, but with maths when the questions are really tough because the problem may be totally abstract and have no relation to real life how are you supposed to guess at what to do? If I have an integral that I forgot how to solve I can't go "right the integral is on earth so it's subject to a gravitational field at x angles so will have to do this, this and this" You can do that in science.
2) Chemistry - Easily the toughest science, you have to be competent in a wide range of areas and unlike with Biology you can't get away with memorizing the book.
3) Biology - You can get away with memorizing the book but for the top marks you do need to be able to apply your knowledge in a novel way. but it really depends on the exam board you use at the end of the day. AQA started out as a "memorizer" but halfway through **** got serious when they stepped up their game and came up with that infamous January 2010 exam.
4) Physics - Easy as **** end of story. I just 'get' physics and I got 100% on half the exams. Before you call me arrogant do realize that I just openly admitted to sucking at A level maths.