Is there any speed difference between these two versions?
<?php echo $var; ?>
<?=$var?>
Which do you recommend, and why?
Performance difference is insignificant. Moreover, with use of APC, performance difference is zero, null, nada.
Short tags are problematic within XML, because <?
is also markup for XML processing tag. So if you're writing code that should be portable, use the long form.
See short_open_tag
description in http://www.php.net/manual/en/ini.core.php