ICO is open to everyone, while IEO requires people to buy their tokens using the exchange accounts. But the biggest problem with ICO is not being monitored by any third party or anyone else. Scams and frauds follow ICO. Because of its open nature and not being linked to exchange accounts, ICO is subject to more frauds, as scammers can directly exploit this weakness without the involvement of any third party. These scammers promised many people but did not deliver the result. Putting all these things in mind, I think IEO is much better.