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

@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?