When I write it for personal use, I use Year-month-day. This is the standard in Japan, but I use it because it's the most logical and consistent with number systems in general;
After all, if you write 123865.2 The least significant part is on the right, and the most significant on the left. And in a date, the most significant (largest) part is the year, and the least significant is the day.
Of course, since my chosen format goes against the standards of every country I've ever lived in, when dealing with official documents I write it Day-month-year, as dictated by the standards of most countries.