The best method to use to convert a Date to a String in the current user's locale is Date.format. This method returns a String that represents the Date in the format of the current user's locale. For example, if the current user's locale is English (United States), the Date.format method will return a String in the format of MM/DD/YYYY. The String.format method is used to format a String with placeholders and arguments, not a Date. The Date.parse method is used to convert a String to a Date, not the other way around. The String.valueOf method is used to convert any type to a String, but it does not take into account the current user's locale. Reference: [Date Class], [Apex Developer Guide]