I've read many like the AES/EBU for digital and it's becoming more common in both digital interfaces and external DACs, its the studio standard for digital. low noise due to common mode rejection.
I use digital coax and it sounds great, optical sounded thin to me. I use a gustard U12 USB interface that has it's own low noise PSU and extremely accurate clocks. It's based on the XMOS chipset. I use a canare "True 75ohm" coax, I've been told BNC is the only true 75 ohm interface but my gear doesn't take BNC and I can't believe that adding BNC to RCA will do anything but degrade the signal..
worth mentioning is i2s, it's digital audios true signal and removes the s/pdif transmit -> s/pdif recieve from the equation.
i2s word clock is separate from the digital signal so in theory it should have less jitter. the only dacs/digital interfaces I've seen that support i2s are niche RPI based devices and audio gd/gustard. i2s unofficial format is HDMI but anything can be used in theory as its just a series of pinouts. Expect i2s to gain popularity as companies scrape all the fidelity they can from digital audio.
i2s is pretty cool in DIY applications and is very affordable- more info here
https://volumio.org/raspberry-pi-i2s-dac-sounds-so-good/
IMO the chain of digital components is more important than the connection type though. Having USB decoupled from the motherboard bus, having high quality power supplies for your interfaces and a high grade clock are vital.
When I bought an external digital interface (gustard u12) it dropped noise floor and added to fidelity, subtle improvement