My ranking from hardest to easiest would be:
- Electric Power (U4O1) [mixture of a lot of theory and for the most part - boring content]
- Sound (U4 - Detailed Study) [kind of boring]
- Special Relativity (U3 - Detailed Study) [pretty easy actually... the other stuff isn't that hard either]
- Motion (U3O1)
- Light and Matter (U4O2)
- Electronics and Photonics (U3O2)
Most interesting (to me) would be Light and Matter and Special Relativity.
Electronics and Photonics was extremely light weight - it didn't even feel like I learnt anything there.
Electric Power is pretty theory heavy, the right hand rule is kind of weird as well - it doesn't feel right to me (and can be awkward sitting there trying to figure out which way current is going). I haven't done too many trial exam questions yet, but the textbook questions for Electric Power are pretty damn boring.
Motion is pretty maths heavy - but pretty boring overall (in VCE Physics anyway). There are a few interesting questions out there. I think I spent too much time studying motion (my hard work didn't even pay off for the exam...

), sometimes I find myself just thinking about things Newtonian physics-wise...
Sound isn't too bad, just builds on your knowledge of waves really. Questions aren't that fun to complete for sound.