Gross rental yield refers to the total rental income as a percentage of the property's purchase price, before deducting expenses such as property management fees, property tax, insurance, and other costs. 

Net rental yield, on the other hand, refers to the rental income after these expenses have been deducted, providing a more accurate representation of the actual return on investment. 

The net rental yield is typically lower than the gross rental yield.

A good rental yield in Australia can vary, but generally speaking, a rental yield of 4-5% is considered average, while yields of 6% or higher are considered high.

The highest rental yield suburbs in Australia can vary based on market conditions, demand for rental properties, and property prices in a given area. 

In general, capital cities tend to have a higher demand for rental properties, which can result in higher rental yields. 

However, regional areas may offer lower property prices, which can result in higher rental yields when compared to capital cities.

However, some suburbs that have historically shown high rental yields include:

Darwin, NT: suburbs like Stuart Park, Malak, and Wulagi

Hobart, TAS: suburbs like Rokeby, Mornington, and Warrane

Adelaide, SA: suburbs like Kilburn, Holden Hill, and Pooraka

Perth, WA: suburbs like Armadale, Balga, and Mirrabooka

Sydney, NSW: suburbs like Auburn, Wentworthville, and Green Valley

It's important to note that past performance is not a guarantee of future results and it's always a good idea to research the local property market, rental demand, and infrastructure developments before investing in a particular area.