The most common answer to this question is, when the housing market is at its peak. However, the downside to this is that if you are thinking of reinvesting in the property market, you will also be buying at the peak time, unless you are prepared to rent for however long it takes for the market to drop. You also have to be adept at reading the market & predicting the future. (Anyone have a spare crystal ball?)
As far as the best time of year, Spring has always been quite popular. One downside to Spring is that there tends to be a lot more inventory to choose from. So, buyers could become a bit hesitant as they may be a little spoilt for choice.
Putting your property on the market in Winter could be appealing as the inventory tends to slow up around this time and buyers from down south in the cooler climates get enticed to come further north for a welcome break from the chill. Your home could possibly be the reason they cement their plans for a change of residence or the purchase of a holiday property.
Summer is also a great time to sell. Just avoid major holidays, as people tend to get busy with family. Make sure that air cons are working & pools are clean.
In regards to Autumn, it is one of my personal favourite seasons, especially in Queensland. However, I do not think it’s a great time of year to have a sales campaign, especially for a family home. The reason for this is that settlement would fall in the middle of the school year & is usually not a suitable time for families to be moving.
