I did physics last year and i'm doing it again this year (accelerated and compounded course, years 11 and 12 in 6 months) so i'm not just plucking this from my arse.
I can tell you from experience that Quanta to Quarks is not the easiest option topic. The questions they ask are relatively simple but it's hard to get that firm grasp on it. If your forte lies with particle physics and the atom then this is the option for you. To get top marks in this, you need to be able to understand the concepts very well + get additional information for certain investigation tasks.
Medical Physics is not only easier but shorter. Questions can get harder but you just need to make sure you do alit bit more research on the net or wherever. So basically to get Band 6 in this option, you need to demonstate you have conducted further research and understand comprehensively what was covered.
Mind you, if you are doing another option in class, do that option and not another one, fullstop.
Hope I have helped.