Forum Default (the first option).
Down here I'm used to using the last two choices. It makes much more sense, actually. What would make even more sense would be to use YYYYMMDDHHMMSS with a 24 hour clock (army time.. haha).
Extra question: does anyone in the States say the date June 15 without using the ordinal version of 15? They do it here and it drives me crazy. They will even say the number and then the month without using the ordinal. "The movie will be in theatres fifteen June." Oh, and "The concerts will start on June fifteen." This is very important to me. So is the usage of "maths" and "sport."
"June fifteen" is sometimes said here. "Fifteen June" is very uncommon in my experience, but then so is "fifteenth June,"- instead it is "the fifteenth of June."