I believe this question has been answered a million times but I will still add a thing or two. First and foremost they are all fundraising methods which the team of a project banks on to access funds from their users and/or investors. Now among all them, IEO is better because it takes place on exchange thus investors will have the opportunity to sell as at when due without having to worry if the team will exit scam immediately funds were raised. Investors will also have the opportunity to participate based on the type of exchange, as it really matters. This exit scam of a thing was found majorly in ICO, this is because with the funds being in possession of the team makes it easier for them to steal. STO on the other hand, have had little or success so far.