DAC connection: which type gives highest fidelity?


Suppose one wants to connect two digital devices, as in a streamer to an outboard DAC or similar.

Which is the highest fidelity connection?  USB, coaxial, or other?

Thanks!
bobbydd
USB async would be the highest fidelity but for the fact that USB sources are often very noisy. Isolation is key and not all USB interfaces have that. Coax normally does though, but it'll be higher jitter than async USB.
The best is probably up for debate I2S, AES/EBU, etc. The worst, in my experience, is toslink. Your mileage may vary. 
My understanding is that different manufacturers have optimized different connections among the available options.  So it's really impossible to generalize about.