I did all three sciences. I found Biology much more enjoyable than Physics (and I consider myself a math guy), but thats just my opinion.
Biology:
-Lots and lots of memorisation. There are like two things that involve calculations and there is little processing work. If you're good at memorising, do it.
-Because it involves mostly regurgitating, its possible to finish the 3-hour exam in under 1 hour if you're of Band 6 material (see below).
-Biolgoy scales very poorly. IIRC, you have to get the top 2-3% to reach Band Six.
- Like all sciences, it involves nature and practice of science questions. This constitutes most of the 'processing work' youll ahve to do
Physics: -Fair bit of working with mathematics, its usually knowing how physics formulae are derived and applying these formula to real-life questions.
-Unlike maths, you do not need to memorise equations. All of them, except for two or three, are given to you in the exam.
-That said, a notable part of Physics involves memorising history of physics and the nature&practice of science.
-Scales a lot better than Biology, the scaling is roughly equal to Chemistry.
EDIT: and like some guy above me said, take a look at the syallbus for both subjects, especially the dot points section of it. In addition to this, I also suggest you look through a few year's worth of past papers, because for Physics many things are tested in the exam which aren't explicitly stated in the syallbus (e.g proving formulas, applying formulas)