Australian one week vacation?

so im planning to take a vacation to Australia in the end of January. its a 1 week walkabout with dinner and lodge included.my question is i can only pick 1 city and its between Sydney, Brisbane, or melbourne. which should i pick. i like to go out at night also.

All three cities have some wonderful attractions but if you have never been to Australia then pick Sydney for sure. Sydney has one of the most beautiful harbours in the world and in your week you will fill the time in beautifully. Take a day trip to the blue mountains and visit Bondi beach plenty of places for some super walks . You will love the walk from Bondi to Coogee beach. a walk around darling harbour will make you want to go back several times. so much to see and do here you can walk around to the Opera house visit museums hop on the ferry over to Manley and wander up the Northern beaches. Take the River Cat up to parramatta . visit the markets and china town . walk on a glass floor above the city at Sydney Tower . the list goes on and on
Brisbane would be my next choice but I would spend most of the time on The GoldCoast that’s if you love beaches. then they have all the hinterland that is magnificent to visit.