YYYY/MM/DD because it follows the way we write out numbers, most significant to the left.

Also because it's easy to sort in programming.

DM/YYYY/MD

YYYY-MM-DD (aka ISO 8601) is the one true date format. Aside from being ordered hierarchically it has the nice bonus of being mathematically comparable if you strip out the dashes.

Why Americans decided that middle endian is the way to go is beyond me.

DD/MM/YYYY is the best and should be the standard everywhere

DD/MM/YYYY is a terrible system because it can easily be confused with MM/DD/YYYY. MM/DD/YYYY is even worse, but that doesn't change the fact that you don't want another one that it could be confused with. The best is YYYY-MM-DD.

D/m/y is the best, y/m/d is acceptable, but anything other than that is confusing

Hm, the lead zero in the month is critical, otherwise when you try to sort the dates chronologically January will be next to October - also for the same reason I prefer the year first, otherwise January 2018 will get sorted with January 2021, so YYYY-MM-DD is the convention I prefer when I'm going to need to sort

Yes.