well I think both have their own risks. Buying a tokens in ICO is a huge risk, well if it turns out it is a scam you will loss all of your investment on it, also if the ICO wont prosper still your investmen is a waste but if youre lucky and did invest on a successfull ICO then expect you will get a huge profit on it!
but on trading, buying coins/tokens is a risky thing, you dont even know if your tokens are going to grow, but still it minimize youre loss than investing bad ICO.