I will agree that the contest is between C and D. These are both younger Koi judging by shape and in particular the pecs. They are most likely in the 18" range? Here is my standard disclaimer, "You cannot adequately judge Koi from pictures, only pictures of Koi from pictures. I am going to make the assumption that since all of these are being judge together, they are of a comparable size. Thus I have resized "D" accordingly in the picture below. As such, its conformation is not sizeably different than "C". In addition, in younger Koi (less than 18 to 20", conformation is NOT the determining factor as it can be with the big girls.
So, let's look at pattern first. "C" has a traditional 3 step pattern with an offset step of beni on its right filling the gap and adding "interest". It also has an almost perfect odome or "tail stop". D's pattern, although interesting cannot stand up to C's in my mind. Skin quality is next to impossible to judge from a photo as is depth of color to one degree or another. The sashi and Kiwa on "C" is superior to that of "D" and the softness of beni on "C" also outdoes that of "D" (although color can be VERY misleading in photos).
Niether Koi's sumi is fully developed and although "D" has more sumi, as a percentage of developement of the total, "D's" is less developed than "C's".
Overall, I would select "C" as number 1 and "D" number 2, today (based on the pictures....I could do a 180 live perhaps, who knows?)
But, you know what they say about judges? "With one good eye, they could be a cyclops"!
Steve
Edit: I forgot to mention the one disturbing attribute of "C". the leading ray of the right pec is not complete (short).