PHP 5.4 includes a host of new features and many bug fixes. The latest version of PHP was released last 1st. March, between general improvements in version found eg performance improvements, reduced memory consumption, base code "cleaner" because functions were eliminated "deprecated", among others.
WARNING !!: A major issue for users of Windows XP and 2003 systems is that PHP 5.4 is the last version that provides executables for these versions of the Microsoft operating system.