Hey, I currently do Biology, Chemistry and Art at AH. I’d say, it depends on what you’re wanting to do. I know people who do AH Maths and Physics that find it very difficult due to it being content heavy and slightly hard to understand. Of course, you should try and talk to your teachers and people at your school who have done these subjects in order to gain a better insight.
I can only talk from a Biology and Chemistry area - I will say, far more interesting. I don’t know if they’ll be reinstating the assignment for you next year but for us it wasn’t there. Biology - content wise, a lot. If you think your jotter is full now, wait until you get to AH. As for the mark schemes, they are insanely difficult! I got an A last year and I’m sitting at a B/C (it fluctuates awfully) so I’m finding it far harder to revise. As for chemistry, I can’t say it’s too difficult but in my opinion, most of it is just maths. You understand the reactions, the worst part of Chemistry AH is the curly arrow mechanisms in Unit 2 but otherwise, difficulty is not too bad. What makes AH so challenging is the content volume and the time being up against you, so start early! Balancing 3AH with university applications (I needed to do interviews and an entrance exam) was a huge struggle for me but now that it’s dying down, I know I can bump up my grades before exams.
Hope that gives you a bit of help and best of luck with whatever you choose!