It all depends on the situation in the market of crypto currencies. When everything is good in the market, prices are rising, it is better to buy tokens of promising projects during ICO.
Otherwise, buy coins only on the stock exchange. So you can evaluate how well the coin you are interested in is traded.
Yeah, if the market is not in a good position I think thats the best time to buy more good altcoins. If we are in a bear market, its too risky to invest on a small coin so always choose the top coins and wait for the next pump. Investing on any ICO during bear is too risky, better to analyze na market well before making decision.