I'm gonna say that the outback would be great, central western NSW would be good, and as said above the High Country is absolutely stunning at that time of year albeit bloody cold.
As for my beloved Tasmania, naturally there is no bad time to visit, but I would say the best time is March to May with April probably the peak. The large number of deciduous trees in autumn foliage combined with eucalypt forests combine to make great photography, and the light at that time of year is stunning.
It's also the time of best weather, before the cold sets in but after the hot dry summer.
Winter is all about bare branch trees and snow capped mountains, black and white heaven.
Everything browns off in summer.
Spring is often windy with lots of frost and fog and still snow on the mountains, but new growth everywhere looks great too.