They are greatly different STO should be the best as it offered a good opportunity to its investors as share holders of the company STO guaranteed full security it very hard for STO project to dump as it legally licensed even before the token sale as a result you can never witness a scam STO project all like ICO. IEO is just an advance ICO though the exchanges almost play the role of sec for the safety of investors and their own reputation. The project are properly screened before they can be accepted by any Exchange to carry out IEO.