I do three science and two humanities subjects. I've found the science subjects harder because no matter how well I've learnt something, if I don't understand it I can't apply my knowledge in the way the questions require. I haven't really found science marking to be easier either, particularly in biology & chemistry - what you've written can be perfectly correct, but because you've missed out a single word you can miss out on a mark for that question.
History & geography were harder in terms of how much I had to learn for the exams and the time constraints, but writing essays is a lot easier than having to understand, for example, organic reaction mechanisms, because you just need to know how to remember and analyse evidence & facts to write a good essay. Again using reaction mechanisms as an example, you can't just learn the nucleophilic substitution mechanism for a particularly haloalkane & nucleophile, you have to be able to apply it to any two substances given in the exam, and work it through in your head to determine what you will end up with at the end.
I had this debate with two of my friends who do RE & sociology and tried to claim they were much harder than sciences, because of how much you have to learn & how much time you get in the exams. Strangely, when I was sat with them doing chemistry & physics practice papers just before my exams, or whenever I talk about science, they say that it's impossible to understand, yet I can join in their discussions about religion & sociology etc. and still understand most of it. They also often talk about how easy RE & sociology are, which completely contradicts what they said to me. I say sciences are much harder.