LOL. Adelaide is a city. Nice troll.
The best state is Hawai'i, of course. The reasons? It is the happiest and healthiest state in the US. It is beautiful, has perfect weather year round, and a plethora of outdoor activities to enjoy. It is full of many different cultures and has a very intriguing history. The biggest reason, though, is the Spirit of Aloha. You just feel loved by everyone and everything around you as soon as you step off of the plane.
The worst state in the US is Nebraska. Nothing there but corn, rednecks, and the most terrible football team in the country.
In the contiguous US, Utah is my favorite; it has pine tree covered mountains to deep canyons and rivers to sandstone mesas & bluffs carved into sculptures by time. Least favorite is Ohio, snow turns black in Metro areas (back in the 80's), flat and very industrial. Most states have unique qualities, some you have to look harder than others.
You need to be clearer in your question, do you mean States in Australia - lets face it, we've only got six plus two territories, or States in other countries! If you mean Australia then perhaps you should post in the Travel-Australia section.