I'd say go for kiting go to Perth in summer and cairns in winter! Perth gets deabreezes in summer and cairns gets trade winds in winter! Cairns has a nice backpacker feel to it so heaps of nightlife fun. It is also cheaper than Perth. However in some seasons you can't swim in the water in cairns due to deadly jellyfish, sharks, crocs etc. However I think in winter it should be fine. The thing I love about cairns is that it tropical and surrounded by rainforest. Beautiful nature! Perth has totally different nature. More 'australian' lokking I guess. Also keep in mind that it rains often in cairns! When you're there though also check out all the places birth of cairns like port Douglas and cape tribulation.

So as I said Perth in summer cairns in winter!