What's the best (or is there a "best") DAC input to use?


Many DACs have all or most of the following inputs: USB, Toslink, Coax, BNC, AES/EBU. Is there a "best" or "preferred" input to use (i.e. which input should theoretically produce the optimum performance) and if so, what is it?
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USB theoretically should be the best as long as it is asynchronous.  As name suggest D/A converter clock is completely independent from the computer. Data is sent in chunks (frames) while DAC sends back signal "Buffer over/under-flow" used by computer to adjust size of the frame.  Of course USB cable can inject unwanted electrical noise especially when DAC is powered form USB.   It is desired to use cable without power wires, when DAC has own supply, but even then there might be some amount of digital noise on the cable.  Still, I would start with USB first.  

Choice between Toslink and Coax is not so simple.  In most cases Coax should be better, but it is system dependent.  Toslink, being optical, cannot create ground loops, but has slow transitions.  Slow transition thru threshold point combined with system noise can create variation in level recognition moment - a time jitter (noise in frequency domain).  Faster transition in coax can cause reflections on characteristic impedance boundaries, that can modify (add to) shape of transition thus causing jitter,  It is a function of all impedances and expensive cable won't necessarily be better.  What works in one system won't work in another - you need to try.  Pick at least 1.5m long coax cable (reflections will come too late to add to transition) or very short cable <12" (no reflections).
@kijanki 

Thanks for your rather informative response. From literature I read from DAC manufacturers, it would substantiate your claim that USB should theoretically be better. For instance, the Schiit Yggdrasil manual indicates "USB is great for audio. Try it, you’ll like it" and elsewhere in their manual go on to write "...buy a better transport.
Or use USB". 

I glean they at least prefer USB. Again, thank you @kijanki  
You're welcome.  At the beginning USB was used as synchronous meaning D/A converter clock was derived from unstable computer data rate (to avoid loosing or gaining too many samples).  Async USB should be better.

Be careful with "better" transports.  Some of high end transports have fast transitions, in order of 5ns, making cable impedance match critical.  In such case using very short wire (that is not considered electrically "long") is pretty much impossible.  Rule of thumb says cable becomes transmission line (reflections) when its propagation is longer than 1/10 of transition time.  1/10 of 5ns would be 0.5ns equivalent to 10cm of wire (assuming 5ns/m) including connections inside of transport and the DAC.  On the other hand fast transitions reduce influence of electrical noise.
AES/EBU, a professional interface that was likely used for the master your music is derived from, will be best

USB is problematic in practice - besides the noise issues noted above, there can be ground loop problems

Toslink avoids the above, but...

then there is the issue of Redbook vs. Hi-Res

Schiit has a new product Eiter(?) and there is the Iso Regen, etc. and no doubt other manfs. have things (besides hyper-$$ cables) for USB

I would investigate the 2 boxes as both companies have return privileges
BTW, Firewire was good

the future is not always better
AES is best in my particular setup.
I have tried almost every connection for a DAC.  Of course, it depends on what the DAC will accept, but over the course of at least 100 DACs, this is my take on the best:

1.  I2S
2.  Firewire
3.  AES/EBU
4.  Coax with BNC
5.  Coax with RCA
6.  USB
7.  ATT Glass Fiber
8. Toslink
Very enlightening responses by all. Sincerely appreciated. Besides the fact that the DAC itself often wouldn't have every conceivable input, the transport also wouldn't have every conceivable output. Amazing how this hobby's possibilities and the quest for audio nirvana is seemingly never ending, because given the responses thus far, finding the right combination of DAC, transport and cabling between the two can be rather challenging. 
I2S IN THEORY CAN BE BETTER THEN ANY TYPE OF USB
For on the 5v wire potential electrical noise ,depending how well it is isolated.  If your dac does not depend on this method  then 
It can be as good  . Ps Sudio has tun this debate for awhile.
EVEN their very gifted Digital engineer Mr.Smith agrees 
Both are close .BNC can be excellent also everything comes down
To how well the Digital products deal with every facet of the  signal. Both Digitally,and Electrically.
@audioman58  perhaps then I should ask if in this case *theory* translates into any real perceivable audible advantage. And @mofimadness , I wouldn't have the luxury of trying 100 DACs. I'm trying to get a potential purchase right the first time. I suppose what I'm wrestling with here is if I'm to buy a reasonable good DAC (like the Shiit Yggy) and then use a reasonable good transport (like my Oppo UDP205 or maybe even a Blue Sound Node 2), do I now need to be *overly* concerned with how I connect the two? 

And when I *look* (not buying one anytime soon) at high-end DACs like a Lampizator Big 7, even they are not offering an option to add I2S or firewire as an input option. So what commercially available DACs have that input?
I also have tried them all with my Master 7 dac and I2S is the best. The rest are close but I would avoid Optical or Toslink . By the way I use  a standard usb cable from laptop to a Singhzer USB converter. Then go from it with an Eithernet cable to my dac. If the dac your going to buy has BNC coax I found that is also very good. Also follow for starters the suggestions of the dac manufacturer
Alan
I2s, would never go back to usb

To GDhal .Anything Schiit does Mike Moffett knows his S..t.
Oppo 205 decent dac for the $$ personally  the PS Audio 
Offers this I2S as a $800 add on board which is total B.S.. 
I recently bought their top Direct stream dac ,that is a Excellent buy 
With free firmware upgrades,the latest Huron was Very good.
When you are buying a $6k dac Retail can be bought for $4k .
Total rip off to not include board for I2S  board.if you are using s digital player make sure it has one most do not. They do claim it 
Sounds a bit better .i will never know ,just on principle.
One more thing I have tried a Bunch of good USB cables I like the 
as Diamond a lot. There is a U.K cable that is more refined and a bit richer at the $1200  Mark still testing it 
I would avoid Optical or Toslink


Why?