I2s is the best, followed by anything else, I used Ethernet before i2s, last is usb. My $1000 i2s cable is .75 meters long. A lot of the better dacs are not including usb, while some like Berkeley make a $2500 box to try to make usb sound better. https://www.berkeleyaudiodesign.com/alpha-usb2
Most people when asked this question state usb sounds better because they have never tried i2s. Why? because most dacs don’t include it, and most servers/streamers don’t provide it. The better products do provide i2s. Over a couple decades, when you saw the proprietary digital cable going from an sacd player into the preamp/integrated (like what Esorteric es-link provided as an example), was using i2s.