Many DAC manufacturers insist that their Ethernet input is best, and we are often asked why we favour Digital Outputs over USB. Confusion arises because in many cases the user is faced with a music server and a DAC that both support a range of possible interfaces between them. The user naturally wants to know which type of interface sounds best.
But the issue is not about alternative types of connection. It is actually about alternative solution architectures. For example, using Ethernet means that the Player (endpoint) is in the DAC; using USB means the Player is in the music server; using synchronous connections (I2S, S/PDIF & AES3) means the Async to Sync conversion and re-clocking is in the music server.
Your choice of connection shifts individual roles between the music server and the DAC. Where each role is better to be performed depends on the actual music server and the actual DAC.
Please read our Design page for a simple explanation of how there is no hierarchy of better/worse sounding connections, and what it really means when you decide to use one type of connection over another.