Both are a shoppers paradise. When you are shopping in Hong Kong remember it is very much a case of "buyer beware". There are a lot of 'knock off' copies there that look like the real thing so you take your chances. Generally the big department stores are OK, though ... and there are plenty of them! Best bet, just wade in, have a great time and be careful ... if you buy something electrical it may not have some cables with it, check that it works on Australian currents, etc. .. a camera - check that everything is there, etc. etc. etc. All just common sense, really ... and don't forget to watch when / if it gets packed away that nothing 'disappears' from the packaging once you have agreed on a price.
Have a great trip and you'll have a ball - be warned, though, it will be humid cold in Hong Kong at that time of year so take some warm clothes with you.