I think I'm selling mine when they go under 400$, which I hope will never happen, but might even happen today the way it's going down now.
On the other side I think I will sell them at around 900$
I sometimes sell Bitcoin when the price is rising and when I know that I can make a profit because you are not going to sell when you cannot make a profit.
I do not sell all of them because when the price is rising there is always a change that it will rise even further after you sold.