Which type of cable sounds best for Streamer to DAC: AES/EBU or DIGITAL COAX or USB ??

As said, it depends on the components involved. You can ask the manufacturer or just see what sounds better to you.

USB has the advantage of handling higher sample rates. SPDIF or AES3 are usually limited to 192 kHz. USB does much higher. (It doesn't matter to me, but it might to you.)

Could one use an HDMI? I have an HDMI running from my source, whether it be my phone, tablet, or MacBook, to my oppo.

No idea on the HDMI, but when one considers the work put into the AES/EBU, coax and usb, with regard to taming sources of jitter and whatnot, on those three formats..

..and that HDMI is a complex system, more complex than the others and exists purely at the consumer level....

...and has had no jitter and noise taming for audio, in the high end direction...that no devices, chips or schemes to tame high end audio problems in HDMI exist...well..it clearly marks HDMI as the inferior audio data transfer format. all for a plethora of issues and potential issues, that are not easily detailed in simple posts on forums.

USB has the best potential, when they are properly isolated, and well engineered.

Optical removes ground loop issues which can cause excessive jitter. Good choice from a PC/laptop due to power supply grounding issues.

Ethernet is also a good choice, as it is specified ad highly isolated. Use shielded cables if you are worried about EMI/RFI noise.

Cool. I wasn't championing hdmi, I was just asking from a novices perspective if it was a viable transfer medium.