I can't comment on Melbourne but I've done Western Australia. Swim is awesome..perfect water temp for wetsuit swim, crystal clear, super ez navigation. Bike is 3 loops, scenic, pancake flat, road quality fair, got increasingly windy as morning wore into afternoon. Flat is fast but not easy...no break for the legs, you must pedal every inch, need to remember to stand up out of aero and stretch periodically as the course will not do it for you. Run is also pancake flat, 3 loops much of it on bike path. The year I raced was *very* hot (~100F) and run has little shade. Beautiful, well organized race. I loved it...race management has changed and I don't know if that has affected the race.
I doubt you'd go wrong picking either.