Which Cable Makes the Biggest Impact?

IMO…

1. Power cables - for power conditioner, amp, source components 

2. Speaker cables

3. interconnects 

4. digital cables (whatever the connection method…USB, ARS/EBU, etc.)

5. Ethernet cable to streamer

All with a caveat that you have all the critical stuff (top notch components, speakers that you really like  and your room acoustics) in order. I wouldn’t worry too much about cables (isolation devices, or footers too) if any of the above critical items aren’t taken care of first. Cable swaps are easiest and most of the time the cheapest changes we tend to gravitate towards but as long as you have decent, neutral basic cables like BlueJeans or Mogami, worry about room acoustics and components first. 
Just my $0.02 based on my experience and how far into this hobby I am at this point. 
 

@deep_333 I don’t thing $100 is a point of diminishing returns for anything in this world right now…although it would really be nice if that was the case!

Unfortunately - my impression of biggest impact is clouded because the order I experimented.  I think the answer might be 'where ever you start'.

I started with speakers, ICs and power cables.

In each case they made an impact resulting in me continuing to experiment and listen.

During my experimenting with speaker cables I used mogami XLRs and the OEM power cables. 

• The speaker cables had an impact on sound stage and clarity.
• IC's improved details
• Power cables improved details especially in the lower frequencies.  

And for the record I would have been really happy to not have heard a difference!

@overthemoon I tend to agree, and much earlier in this thread suggested that the last cable added was the most important because you had taken care of issues elsewhere and now you were more fully experiencing and expressing the benefits of the next addition.  I got called out at the time for being somewhat naive as each cable has it’s own function in a system and therefore can only have so much effect.  
 

My answer to this criticism many years later, having a better system, a much, much better room, and much more experience tweaking, is “whatever”.  It all matters, and matters in different ways depending on what specific “problems” you are trying to address to preserve and keep signals in their lanes in your room and set up.  I generally agree with the original premise that power cables make the biggest difference, and have now assembled and used many from different bulk cable and connectors, and have also used many PCs built by others.  What I find is that different cables can make both revelatory and frustrating levels of difference depending on the system and application with different equipment models and types.  But in the end, the effort is definitely worth it.

I am also blown away with the difference digital cables make.  I just swapped a USB cable from a SSD to my streamer and was gobsmacked. 

YMMV

kn

I am also blown away with the difference digital cables make. I just swapped a USB cable from a SSD to my streamer and was gobsmacked.

Well, looks like I may be in for a treat. Just ordered the Wireworld Platinum Starlight 8 USB..

In my limited experience, the current rank from largest to smallest difference.

1. Power cord

2. Speaker cables

3. Interconnects

4. Digital cables (USB)