I enjoy developing in PHP 5, for its improved object oriented design and XML support. PHP 6 is slated to have additional useful improvements like built-in Unicode, built-in caching, and increased security out of the box (no register_globals, magic_quotes, or safe_mode).

Here are other improvements I’d like to see in a future version of PHP:

• while-else statement — A while-else statement would be perfect for MySQL results: loop through the results, or if there were no results display an error.
• a better toString() — The toString() function lets you cast an object as a string, but in PHP it only works when directly combined with echo or print. Dumb.
• function overloading — Let the signature of the function call decide which definition to use.

Read more about PHP 6.