It is no longer a question of timber OR aluminium, many houses now use a mix of materials depending on the look and feel for each room. When choosing between timber and aluminium, consider the style of the house, maintenance required, energy rating, BAL rating and price.
The main points to consider when choosing between timber and aluminium are the maintenance, look and material qualities. Timber windows and doors require more maintenance but offer greater energy efficiency than aluminium. Aluminium requires very little maintenance and can achieve a better bushfire rating. The visual difference between timber and aluminium windows is a personal preference.