IEO simply better because there is a guaranteer. And it comes with a guaranteed listing on an exchange.
But you are buying the same token. So if the project is shit, IEO won't be enough. You will end up losing money.
Many recent projects are all very low prices and the IEO is a very risky investment channel if you choose a project listed at the new exchange. I think now IEO is getting more and more and that makes investors more dangerous when investing. Most recently, the Ocean at Bittrex has a very low price and it makes things worse so IEO will soon die in the near future.