When is the best time to visit Australia for good weather?

In our house we follow this:

Autumn/Winter - which is about May to September, we travel north.

Summer - which is from about September to March, we travel south. Tasmania and Victoria are the best, but can still be hot. Western Australia can be coolish down south in Summer. South Australia is hot in summer.

The hot rainy season is between November to April and although Kakadu in the Northern Territory apparently looks beautiful in the Rainy season for most the humidity is unbearable if you aren't used to it. Also many parts up north are closed due to flooding at the time. Best to plan your time in Northern Australia for May to October during the dry season as tourist season will be on and all the tourist attractions will be open and the days will be warm around low 30s Celsius and the nights will be a lovely temperature. I hope you have a lovely honeymoon.

Brisbane and around there (south east Qld) is probably September. Generally pretty dry, lovely days, coolish nights but not unpleasant.

North Queensland / NT and northern WA, are mid-year (May - be gone by earlier to mid September). After that, go south - later September / October for Sydney, October-ish for southern Australia (Victoria, Tassie, SA and WA)

If you are going to tropical northern Australia, May to September is the dry season November to March is the wet season and September and October are transitional with rainfall increasing. Darwin and north Queensland are warm and you'll live in shorts and t-shirts. In July it might get cool enough to require a sweater in the evening. If you go inland, however, it can get cold over night although it is fine and warm during the day.

If you are going to southern Australia, summer is the best time to visit when it is hot and dry. Winters can be cold and bleak.

July and August are winter in Australia and a good time to visit Darwin and Queensland. Even if it is winter it will not snow in Darwin or Northern Queensland. Will be cold at night and warm in the day time.

The 'wet' in Darwin, which also coincides with the highest heat and humidity is from November to April and the wettest and hottest times in Queensland are similar. The best time to visit both places is between May and October though late May can be fairly cool in southeast Queensland. How long do you intend staying in each location? If you're only here for a few weeks, I'd say October would be your best option as it's also outside 'stinger season' in North Queensland.

In the Fall or Spring

Darwin, Queensland and good weather are mutally exclusive concepts. You'd be far better off visiting places like Adelaide, Hobart & Melbourne in either November or March.