PHP: PDT vs Zend
I've used Zend Studio for years, but don't use most of it's features - PDT is a freebee plugin shipped with Eclipse (which Zend is built on) that offers the basic functionality.
There is a comparison on the Zend web-site, which seems a little misleading.
As I don't work on huge projects (and generally use naming conventions) I have no need for automatic re-factoring, so I can't comment on that.
The rest seems fine - Syntax highlighting, code hinting and PHP Docs. The only thing I've encountered so far is the code formatter is not customisable with PDT. Fortunately, somebody has written a plugin that gives us all that lovely functionality and it can be found here:
I'm a big user of the Smarty template engine, something that I wish Zend Studio would support - but again, there is a freebee plugin that provides basic syntax highlighting (no hinting I'm afraid) which works with both PDT and Zend: