last year's VCAA biology paper was definitely more difficult than usual (this is subjective tho), comparatively easier papers would include 2013 and 2015.
personally i thought from past 4 years (last study design) it was
2015 > 2014 = 2016 > 2013 (2015 being the hardest - although that was my year so may be bias haha) and I didn't do the 2016 exam in full exam conditions
looking at the grade required for A+ it has been
2013: 93/110
2014: 96/100
2015: 91.5/110
2016: 94/110
but then again really up to personal preference
Cheers!
Would you know any VCAA/commercial exams that would be considered hard, and ones considered easy? I'd like to compare the difference 
STAV are really good papers , they are roughly VCAA difficulty baring a couple fo SA questions i think
insight are alright on the easy side
NEAP good but are tougher than usual iirc
tssm/tsfx - not that good i think on the easy side
not sure if i've missed any companies