Calculus isn't that long and is worth a ton of marks. ditto for Probability and Statistics. Co-ordinate Geometry is short (not necessarily easy) and comes up every year for 50 marks. Trigonometry is insanely popular for how easy and short it is. Geometry is a garaunteed 25 marker.
Financial Maths and perhaps Induction are the only two that I wouldn't really bother with. Unfortunately, unlike other subjects, there is no longer any choice in Maths so having a broad base (but not really understanding much of it) is far more important than having a good understanding of a few. You coyld potentially get up to a H3/H2 even by approaching the subject like that (it's different for other subjects).