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.
coins that have entered the exchange market stage are usually weaker than ico prices, and this often results in losses if the volume of coins continues to weaken.
But to deal with this there is another solution where coins tend to circulate earlier in the forkdelta and idex and many sell cheap, there is an opportunity to get as many of these ico coins as possible, but still have to remain prospective for the intended coin.