It depends on your investment goal. Is it short term or long term?
There is risk on both side of investment but the risk is more on ICO investment than Altcoin investment. ICO, if investted in a good project you could make good money but the question now is how to identify the good projects. There are some threads on that if you search around, though you will need some patience because I clasify ICO to be long term. I guess when you mention altcoin investment you seem to refer to altcoins listed on exchanges right? If so, you need to study how to buy, sell, understand charts etc on exchanges. Buy HOLD or buy and place a sell order. The profits here might not be much since the project might be trading higher than its ICO price. But if it is a long term project which concluded its ico not too long again chances are that the trading price might be lower than its ICO price before the complete development of the project.