Biology, Psychology and Sociology studentsWatch
I'm currently in year 12 (so haven't done much of the course) but biology and psychology are both really fascinating! For biology, the actual information isn't very difficult, but the style of exam questions (for OCR anyway) is much different to GCSE so it takes some getting used to, but overall it's really great. Psychology is also interesting and I think it's generally been really simple; the style of the exam questions aren't difficult at all and as long as you learn the information, you'll do extremely well. No idea about sociology though, sorry
Biology - B - Hardest (one of the most difficult A-Levels to take)
Sociology - B - Easiest of the subjects I have taken
Psychology - A - Not the hardest but not the easiest either (bearing in mind I took it for GCSE, so I had a good foundation)
Psychology is great, I've had experience with both OCR and AQA, it's probably my hardest subject. Content totally depends on which exam board you do though.
Sociology I found incredibly dull and dropped after six months so can't really comment on that, although it didn't seem too hard.