What are the top 3 USB cables being used today in reference systems?

These are called snake oil screechers. It’s a hobby on itself. No need to even have an audio system or even listen to any music 

https://uptoneaudio.com/products/uspcb-a-b-adapter
Shortest possible link, power line separated or completely cut from signal lines on separate layer of the circuit board. Add an Intona USB Isolator for galvanic isolation and save lots of money compared to exotic cables.

If one owns a DAC that has internal USB power supply such that the USB cable only carries the signal and not the 5V power, how does that enter into the question of what is the best USB cable? 

As usual PBN AUDIO is on the money :)  PT Barnum said theres a Fool born every day - or is that a suckered? 
Whats the rest of your system - so this question can be evaluated correctly ? 

I've been using a Platinum Wireworld with ISO Regen and LPS 1. The Regen offers Galvanic Isolation. Planning to combine a Sotm TX USBultra with the ISO Regen.