I will prefer to buy later on the exchange when I observe the project market demand, the type of exchange listed, any developmental plans by the team. Etc. I won't risk investing in ICO and then deal with exit scam projects.
If the project is good then the price in the exchange will be expensive, I prefer to invest in the ICO rather than the exchange, but choosing a good ICO is important because of the many scam projects, and one ICO that we deserve is AMMUT.