As posted to FB by me in response to seeing a European date on one of her pictures:
The dd/mm/yyyy is much more logical than our backwards mm/dd/yyyy format, for sure. Littlest unit to biggest. Makes sense.
For my own file-naming needs though, I prefer the YYYY-MM-DD (biggest unit to littlest), because than one can find one's files, based on their assigned name-related dates, versus just their file system dates, which may not jibe with their content. E.g., if one waits months, to transfer pictures from a camera, to one's computer, the file dates might not reflect the pictures' actual taken-on dates, but such a naming convention preserves that information and allows the 'Sort by Filename' option, in one's folder, to effectively show a chronology.