What is the best digital cable?

Your question is very general, not sure if you will get any useful responses that will help you in particular. I have tried 4-5 of the usual contenders in the $250-$300 retail
range, and to me the AZ Mc2 was the winner. Extracted the most detail with a smooth/natural sound no other cable I tried at this price could match.

Now if you are talking about price is no object, then there
are other cables that I am sure will beat the AZ Mc2, but you never stated what price you would pay.

I would stick with 1 meter cable, it would be hard to sell
.5 meter, and I doubt you can hear any improvement. I have
read some places that claim toslink cables sound better when they are 1.5 meter, but I don't use toslink only RCA.

As you know, "best" is very subjective. I sure like the Stealth Varidig -- I have the 1.5m balanced and the sound is very clear.

for me, the really best ones on my system are:
syn.research squared ref.,xlo LE.,kharma grande ref.
for my taste ,i maybe love kharma more than others,
i did not try but people says siltechs new g5
digital cable also is very good.
some dealer and factory say that digital cable must be 1.5 meter and never less than 1 meter

I compared the Madrigal AES/EBU directly to the comparably priced Cardas (each about $300. MSRP) AES/EBU-- each one meter. The Madrigal was extremely detailed but lacked pace, rhythm, and timing. This was between ML 37 transpot and ML 360S DAC. The Cardas did not have the detail of the Madrigal, but PRT is excellent and thus it is much more musical. I own the Cardas. I too doubt you could tell .5M from 1 M length. Good Luck. Craig.