For the best chocolate in Sydney you have to fly to Melbourne
... in true FT style. Ganache is on Collins St. in Melbourne with some superb pralines (equal to the best in Brussels or Zurich); the owner is chocolatier from Denmark. They also make very good hot chocolate (drinking) for a bargain price. Just William in Paddington mentioned by bensyd is superb and worth a special trip, and makes a more English style of chocolate. A big step down are Koko Black and Haigh which is more like See's in the US (good candy but not fine pralines). I used to fly from NYC to Brussels to buy Neuhaus pralines there, as the ones Neuhaus sold in the US were simply not the same
Now I would fly to Paris for the best chocolate (very competitive field, this fine chocolate making).