Originally Posted by
FlyerGoldII
Being a Canadian, I would recommend AC/Aeroplan. But for any status, you need minimal miles and money spent on AC metal - although I believe the requriements are less for non-Canadian residents than Canadian residents.
AQD requirements are halved for non-Canadian addresses, but Canada is not in a convenient location to get anywhere from Australia, so there's no point crediting to AC unless OP already makes regular trips to Canada.
Since you fly to the US at least once a year, I would go with UA. Based on your travel patterns, it looks like you should easily hit 50k *A BIS per year. Lack of lounge access doesn't really matter if you don't travel domestic US itineraries often.