I won't recommend you both the methods. Buying during an ICO and after the token is listed on exchanges is not a good strategy. The first thing that you should do is research about the token instead of just buying the coin in the hopes of its price increasing after getting listed on the exchanges. When mostly the opposite happens and the price drops by half after getting listed.
Yeah of course buying during an ICO is the best way to make the profits because as usual, coins will be cheaper when they're at the ICO and will be more expensive after that .