What is the most important cable in your system

Between the pre and the power 

I use to firmly believe it was the cables between my preamp and my amps were most critical. Then over years with more testing found the cables between source and preamp matter a lot too, more so. However, recently went back and started rotating in/out different digital SPDIF/Coax cables between my digital sources and my DAC, noting real differences  - more so than I previously recalled. 0s & 1s, right - no, there is more. By default, in my system the most important cable in my system starts at the source. Trickles down from there. I suspect opinions will vary just like different levels of quality sources do.  

In a good streaming system it’s the Ethernet cable between switch/filter and streamer. Btw, a lot of analogue cables benefit from the Schroeder method of doubling up. This particularly applies between Dac and preamp/amp.

I’m using XLRs but I have one better than the other not that the other one is inferior , was just curious what people favor as the best position for optimal sound , we all know that garbage in gives you garbage out but what’s the most critical connection, between dac/ pre or pre/ amp