Very debatable. I've always found YYYYMMDD to be the most pertinent format as it gives you the "most important information first". As in, DD is unusable if you don't know the month, and the month is unusable if you don't know the year.
I like to picture a world where everyone use YYYYMMDD, the Metric system and English for technical terms (I'm from France and I hate when we invent new terms for technical terms).
Y-M-D and D-M-Y both have their advantages. Unfortunately my compatriots have standardized on M-D-Y, a convention that has no advantages that I can think of.
You get the 2nd shortest duration first (tens of days) then the shortest (days) then the fourth shortest (tens of months) then the third shortest (months) etc
With the ISO standard every character symbolises a larger duration than the one that follows, so to get a strictly increasing order you have to reverse the string entirely - today would be 92-11-3102
Today could also have been a "perfect prime day" if MM, DD, YY and YYYY had been prime (in addition to the above). But it's not the case...
11 -> is prime
29 -> is prime
13 -> is prime
2013 -> not prime (3 x 11 x 61)
Too bad! We will have to wait another 16 years before we have a perfect prime day...
