In almost every ICO I participated in the option of distributing the unsold tokens to investors was the reason the price dropped dramatically. Now some will say it is the same for investors because having 10 Tokens worth $10 is the same as having 20 Toeksn worth the same value, but what most people did not see is that the huge drop in price from the initial price is a bad image for any project, also people that did not join the ICO will probably not gonna have this kind of information and all they gonna see in ICO sites is the initial price of the Tokens during ICO and they will compare that with the current price.
The best practice will be to just burn them, it will add more value to the Token, and will make the supply of Tokens less.