Best way for date/time

Due to the large variety of MySQL and PHP date time formats I'd like to have a couple of opinions from people out there ! Building a job database - and one of my fields is of course date time ! Which I want to be able to use latter in show all from last week, last month etc ! Also I want to show the date later in the european from ie day/month/year ! What is the best format to use ?? Thanks in advance reagrds John