As far as I am aware of, the most popular two textbooks for HSC chemistry are the Conquering Chemistry and Jacaranda Chemistry textbooks.
In general, Conquering Chemistry covers the bulk of what you need in a clear and concise manner. It's a very good textbook to use.
It wasn't the textbook my school prescribed though; they prescribed the latter instead. So I can't comment too much on Conquering Chem (however I have seen the textbook before). Jacaranda has the advantage of far more extensive explanations and go into a much greater depth than Conquering Chem. The downside is that its questions aren't always the most appropriate, and sometimes when you just want a few things and not a whole bulk, you'd go for Conquering chem instead.
I haven't found any problems with the diagrams in Jacaranda though.
A textbook is an expensive investment (sometimes second-hand textbooks are expensive as well). If you want to purchase it, go for it. But I don't feel that it's worth the money when other people's notes are across the internet for free.