The question is rather simple. Do you prefer to buy a token when it's in the ICO phase or when it comes out to an exchange?
That really depends. Most of the time I could predict if the token will come to the exchange cheaper then on ICO. There are ICOs which i would not participate and wait for the exchange. But there are some which i invest very early to get good discount. I think both ways are ok as long as you can predict how it will behave on the market. And that is the most tricky moment