There are some very good low-priced I2S/SPDIF streamers that have extremely good specs, like the Holo Red and the Mercury V3. I use the Mercury, which is only $500 and far surpasses the USB output of my Mac Mini server in terms of accuracy and cleanliness. But I don't do extreme upsampling or DSD.
OTOH a friend of mine (who has what I consider a reference system) prefers USB and has a custom-built streamer with JCat USB and network cards. If he weren't happy with it I would hear about it. ;-)
I think in the end it depends on what level of playback you want and if the higher resolution options are worth it to you. It seems like you need to spend a bit more to get high-quality USB output, but that shouldn't stop you from going that route. Relatively affordable USB streamers from SOtM and Sonore are very popular and have good reputations. Then there's Lumin, Aurender and others that seem to be very satisfactory in terms of USB quality. At that point, you need to look at the connection interfaces, which vary in ease and quality. There are a number of threads here about that.
