Participating in ieo is better than buying on the exchange. Once it is listed, those who already own the token will try as much as possible to sell off, and the price will continue downward until it stabilise.
However, for those who do not have time to buy in IEO, it is also very good to be able to buy on the exchange, because there are also new tokens from IEO once listed on the exchange, the price is not the same as the price in IEO, so those who buy directly on the exchange will be more profitable.