Your NBN speed will vastly depend on the broadband plan you choose. The cheapest plan comes with a speed of 12Mbps/1Mbps, while the most expensive one offers a speed of 100mbps/40mbps. The type of NBN connection you have can also limit the maximum speed available to you.
As for ADSL, it can provide download speeds up to a maximum of 20Mbps to eligible customers in selected areas with upgraded exchanges and up to 8Mbps in many other areas, but average speeds will be lower. Actual speeds you receive will vary due to a number of factors such as your distance from an exchange, the network connecting the exchange, your equipment and software and internet traffic.