Digital Audio Output Differences? Is USB Audio Really The Top-notch?

USB is the worst connection you can use, even if you buy into all the gimmicks/tweaks you can buy to try to make it better.

Ethernet and i2s are much better, but only your better dacs include them and they are usually more expensive 

It really does depend on the implementation, but I have never had good results with USB. I have tried USB directly from my PC, from an audiophile server (an Antipodes), and from a number of streamers - Lumin U1 mini, SOTM, Ultrarendu and OpticalRendu, and currently my Bricasti M5. I have used good USB cables - Furutech and Shunyata. I have also tried a number of very good dacs - Chord DAVE/M Scaler, Mytek Manhattan II and currently my Nagra HD Dac, all of which have very good USB implementation.

I always find USB sounds hard, "digital" and unsatisfying. To my ears, SPDIF and AES sound more natural and tonally more complex. I currently use AES from my Bricasti M5 to the Nagra dac. However, a well-implemented ethernet input can also sound extremely good, and was the best input on the Mytyek Manhattan II.

The only way you will know is by listening to them all. But despite its theoretical advantages, USB always seems like a poor choice for audio in practice.

I have a PS Audio Direct Stream DAC.  I've used USB, Ethernet, and i2s with it.  i2s is by far the better option.

If you want to use USB get a DAC or DDC with an Amenero board. This will bring the SQ equal or better to AES/EBU.

It is such a close call using my Musetec 005 DAC with my Aurender N20 I cannot say which one is best only that they are different. Should get my new USB cable today so I guess USB will be better, I'll report back.

Before I got the Musetec DAC, USB was in no way comparable to AES/EBU.

I use digital coax from my Node2 streamer and Toslink from my Audiolab cd transport to my MHDT Orchid DAC. I did a lot of research and asked a lot of questions to both my MHDT dealer and Silnote Audio (interconnnects) and came to the conclusion that as long as the DAC supports the same bit rate quality on each of the port types it should only come down to the quality of your cable. I made sure to get Wire World’s highest grade Supernova 7 Toslink cable (Silnote chose not to produce a Toslink line) since Toslink made me the most nervous for various reasons (neither the streamer or the cd transport support USB), including the bending of the fiber optic cable (I prefer the shortest cable length they offer in this application) with the highest quality glass (not plastic), etc. Toslink will pop out of the port much easier than the other connectors, but one just has to be extra careful not to bump it and make sure it is seated properly each time I’m moving components around a bit. Done right, I think I would be happy with any of the connection options.