I'd say in the area of 160cm, and that's just a general estimate. You can go longer or shorter, and if you aren't a strong skier, getting a shorter size will help you learn faster as it is more forgiving and easier to control.
If you want them to last, go with 171's. If you are just starting out, and will be getting a new set next season, the 163 will be fine, expecially for learning on.
I don't think surface is making a 163, haven't heard anything about that, however jibij has the 171 from this year in stock for cheap, I'd get those if I were you, the size difference isn't that big at all