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).