I just had a I2S streamer bake-off between an PS AirlLens and a Matrix Element S. Neither are either cheap or expensive.
The dac is a Holo May KTE. The Holo May has two I2S inputs which was handy for testing.
Turned off the May's own reclocking PLL circuit so the streamer's clocks were used.
Tested with both Tubulus Libentus and Phasure I2S cables.
Regardless of configuration or what was playing, I (+ discerning wife) thought the Element had the best sound and certainly the best soundstage.
This opinion persisted even when the PLL clocking in the Holo was turned back on again. That was a great surprise.
The main difference between these two streamers? The AirLens uses a VCXO clock while the Element is using TCXO clocks.
I remember talking to the designer of the Musica Capella III and he said that he worked very hard to get the clocking right in his design. I had a Capella for several years and couldn't agree more - perhaps that's what sets the streamers apart.
I don't know if USB or I2S is better, it really comes down to your system. There are lots of Holo owners who prefer USB. I've tested both from time to time and have always ended up on I2S.