This depends on when you use your power and how you use your power.
If you are using your energy gradually throughout the day and have an even energy consumption we recommend a north-facing system that will supply your home with power during the day when you are at home using it. If you are not home during the day and you use your power mostly in the evening when you get home we would recommend covering the north/east and your western roof as you will feed in a lot of power into your import-export meter during the day and you will have the western sun especially in summer when you come home and turn on your air-con this will really help reduce your bill.