The Hunter Valley visitors centre. Photo taken by author.
Over the years I have found that all the visitor centers that I have been to have been very helpful. Especially if I haven't been there before, but if I have and it has been a while they are still great source of information.
My favorite would have to be the one at the Hunter Valley.
I like the Visitor Centre in Hay in NSW. As well as giving great advice to tourists it has showers, an indoor rest area with tables, chairs and a sink,and a lawn area with picnic tables. This centre goes above and beyond.
I find ones in country areas and national parks are often very good, as they not only offer travel advice but also have lots of beautifully-presented information about the natural and cultural heritage of the particular area. One of the best ones I've ever been to was at the Karajini National Park, up in the Pilbara area of Western Australia. The staff were wonderful - Indigenous Australians whose ancestors had been living in the Karajini area for thousands of years, and they had so much respect and love for this beautiful place and lots of good advice for visitors. There were also plenty of beautiful displays teaching visitors about the national park, the lifestyle of the traditional landowners and other interesting things, as well as an wonderful gift-shop and facilities such as toilets, showers, etc.
Another very good visitor centre is at the Morton National Park in the central highlands of New South Wales. The centre was situated in a spectacular location, with plenty of educational displays, a well-stocked gift-shop and good facilities for travellers.
The Discovery Centre at the Valley of the Giants in the Great Southern region of WA is also first-class, with all the above facilities.