Biology:
Pros: Super interesting content (if you enjoy science subjects in general, but I'm biases as biology/science uni student), really helpful if you want to study science, health or possibly med in the future, can have good practical elements (i.e. experiments), plenty of applicable elements to everyday life (especially the immune system topic in year 12), generally a doable subject if you put in hard work and effort (which goes for really any subject)
Cons: Very content heavy, some topics are quite confusing (lots of key terms, fiddly processes, etc.), VCAA questions require very specific styled answers in year 12 (need to learn the ways of VCAA assessors and questions answers haha, but you can with practice), experiments can be mundane/not the most exciting
Design (visual communication and design I'm assuming):
Pros: Really fun and practical, can learn a range of media, quite applicable when analysing and creating designs, can discover areas that particularly interest you (i.e. from the different fields -> industrial, communication, environmental), not content heavy
Cons: So much work (people who don't do folios think it's easy but isn't -> If anything, it was one of the subjects that required the most work, but for me it was mostly fun and rewarding), not usually much exam prep during the year so it's easy to forget the content, VCAA is really finicky with how you answer questions (don't worry about it in year 11, but do keep it in mind when you approach your exams anyway), scales down (but scaling should never be your sole reason to take or not take a subject).
Chemistry:
Pros: Prereq for many courses (i.e. science, engineering, med, etc.), really interesting topics (lots of variety, with some that are quiet applicable to everyday life), good for those who like a mix of maths and content
Cons: Steep learning curve (like AngelWings said), lots of content and formulas, plenty of tricky concepts (especially hard if the teacher isn't great, since you need to be proactive in getting the help you need)
