Personally, i try to buy during the ICO as there is usually some sort of bonus/discount involved. The one you mention here, AppCoins, seems to me to be one of the most promising ICOs of late 2017/early 2018, alongside Utrust. I have purchased tokens during pre-sale as a test and will definitely buy more during the sale. On their telegram group it has been announced that there will be a 20% discount for early investors. count me in