You can use either date or strftime. In this case I’d say it doesn’t matter as a year is a year, no matter what (unless there’s a locale that formats the year differently?)
<?php echo date("Y"); ?>
On a side note, when formatting dates in PHP it matters when you want to format your date in a different locale than your default. If so, you have to use setlocale and strftime. According to the php manual on date:
To format dates in other languages,
you should use the setlocale() and
strftime() functions instead of
From this point of view, I think it would be best to use strftime as much as possible, if you even have a remote possibility of having to localize your application. If that’s not an issue, pick the one you like best.