Winter is actually a good time, as there will not be a lot of tourist , so you have the place to yourself to get a good composition and without people blocking you. But on the cons. it will rain occasionally but comes with very strong clouds and rainbows which brings impact to your photos.
Spring is a better time from September to November, flowers are most abundant this time round, the whole field as far as the eye can see will be full of flowers in the outback. Dolphins, whales and sealion are also in season , you can have fun at the northern part of WA especially with dolphins at Monkey Mia or go all the way to Broome, 2 of the places i did not go due to not enough time.
Summer is way too hot, but depends what you are planning to do, if you are mostly covering the coastal parts, swimming in it is wonderful.