If you're only going to choose one, as mentioned earlier, choose chem as its better for uni (even for med) etc.
If you plan to do engineering however, choose physics.
Physics is largely concept and skill based, once you've got your head around the concepts (which is hard), then the subject should be doable. Physics definitely sounds like the 'cool' science, but it's by far the hardest for many and this can get frustrating.
Chemistry is a decent mix of content and concept/skill and personally, I find it's the most suitable. (I like mixing substances together too, so chem's my favourite science). Understanding chem will help you with certain aspects of other sciences (and vice versa to varying extents).
Biology is largely rote learning, but is a great companion to chem and if you love living things (this includes plants), then choose it. I'm loving it so far (though admittedly, my teacher is amaze-balls). The Y11 syllabus doesn't facilitate much fun, but apparently things get a LOT better in year 12 (defs looking forward to it, so give bio a chance)
If you end up wanting to do two sciences, do either chem/phys or chem/bio since there are overlaps and often one science will help the other (cos chem's versatile like that).
Ultimately it all comes down to interest, and you're going to have to devote heaps of time to any science you choose. Equations should be second nature for chem, helps HEAPS in the 1st and 2nd topics), and although I'm not familiar with the study tactics for physics, you're gunna have to practice heaps. With bio, go over your material regularly so you can keep up to date in class (though this can be said of any subject)
For chem, memorise the symbols (and valencies) of the 1st 20 elements, Fe, Ag, Pb, Cu, Zn as they're the most common elements found in Y11 equations. Also memorise the ammonium (NH
4+) , carbonate(CO
32-, phosphate (PO
43-), sulfate(SO
42-), nitrate(NO
3-), hydroxide (OH
-) polyatomic ions. Sound daunting? Once these are second nature, you'll be able to focus on harder chem content in class, rather than racking your brains for the formula of iron(II) hydroxide.
Chem: you'll relearn some y7 material in the 1st module (The Chemical Earth), but the module is quite fun and does get challenging. Chem in Y11 takes time to get interesting though, and certain topics such as moles etc. can be challenging for SOME (like me. Took me several weeks to get used to them), but fun in the end.
Bio: for all of Y11, you've gotta love your plants! If you do, or if you've got an awesome teacher (I fit into both, yay) then you're fine. Otherwise wait for Y12 or just drop
Physics: Not too sure (I don't do it), but feedback from many hasn't been exactly positive. Syllabus looks interesting though. The subject's half yearly average was lower than that of the other two sciences however. Someone else can help you out with physics though.
One thing though, for any science, pracs count for a
lot more than you think they do. Simply memorising your material won't do it (not even for bio, and certainly not for physics) . If you have any problems, chase up your teacher to iron out any issues (or just ask here). Basically with pracs and skills based stuff, you apply your content (This is heavily oversimplified. Blasphemy, I know)
This isn't the best, and the ungodly time of night hasn't helped it (and neither has my bias toward chem/bio. Phys is cool, I just found it so damn hard in Y10!), but I hope this helps
Science is a wonderfully interesting subject area, and I'm sure you'll love it
Best of luck for Y11/12