Definitely the maths in focus extension one HSC book-it has more detailed explanation of concepts, but in my view, sometimes consulting the Cambridge textbooks will give you the best and most holistic understanding of certain mathematical concepts-for most topics, the Cambridge is better than either of the two books you have mentioned above-at least in my view
Oh my god noooo only use Cambridge. Both those tb aren't good. They help you understand basic stuff and that's all but in cambridge a quarter of its exercise is on basic maths in focus stuff so you can drill it into your head and then it moves on to harder stuff which is really good. Try to do as many of those as you can to expose yourself to a variety of questions. And finally there are the extension questions. Always have a look and see if you can do them rather than completely skipping. Cambridge questions are mad because they're not repetitive Nd you actually have fun doing the exercises. But maths in focus is repetitive and boring and you just blindly use formulas without knowing why or how. Definitely go cambridge and then fitzpatrick is good too.