Between 19 and 25 but it depends on your age and build as well I believe. I'm aiming for around 23 but I have a large frame and haven't been that weight since I was a teenager so who knows, it may not suit me!
If you aim for around 23 it will give you some leeway but reassess when you get closer coz you want to be happy with what you see in the mirror.
Good luck.
x