Finding your perfect PHP editor can often be quite a personal thing, as everyone has their own preferences and style. For years I've used crimson editor as my primary programming app as it was open source (free) and did almost exactly what I needed.

I tried Zend Studio (a proper PHP IDE) a while back and around 6 months ago started using it again more seriously. It's certainly the best tool for the job given the other options right now. A few of the advantages over using a more basic text editor are:

• Integration with the PHP manual (gives hints and function listings while typing).
• Collapsing code blocks.
• Autocompletion for custom functions. This is invaluable when you're working on a large project, it searches though your files and can automatically provide hints while you're referring to functions inside your app.
• Inbuilt versioning. This is most useful, and integrates with subversion or SVN, so you can keep manage files easily from directly within the interface itself.

These are probably some of the the main "must have" features i've come to love. However, there are some bad points, and some are almost deal-breakers for me.

• The Zend IDE is slow. Very slow. I run a relatively new dual core processor, with 2gb of ram and somehow the zend editor manages to be almost painful to use at times. Opening and closing projects can take several minutes, startup times are atrocious, and while open it uses amazing amounts of memory. The GUI is written in java, which may explain this behaviour. Unfortunately the next version codenamed "Zeon" is based on the eclipse editor, and is even slower (after testing some of the trial versions), I certainly will not be upgrading to this newer version anytime soon.
• The tabs are at the bottom and cannot be moved. This is a UI concept that is seen in web browsers, windows, and almost every application that uses tabs puts them at the top. For some reason the Zend IDE puts them at the bottom, and they cannot be moved, they also randomly create new rows, and flip around when you click them - this is very frustrating behavior.
• Drag-and-drop behaviour. I can flip between 5 projects a day easily, and sometimes I simply want to edit a basic config file, or even view a raw CSV file, and I like to be able to just drag and drop a file anywhere into the editor, and quickly editing it. Not "create a new project" or carefully aim it at the tab bar, I just want to throw it into the main window, edit it and go back to the previous file, much like other editors allow you to do.

I really think a ton of improvement could be made in the PHP IDE area, certainly nothing has come out as being "perfect" yet. I think my ideal app would have a snappy interface (i.e. not java-based), have code-completion, collapsible blocks, built-in versioning, a powerful search and replace feature, tabbed browsing ala Firefox style, inbuilt profiling of scripts, a docked pane for browsing files/folders, and the ability to deal with (or at least recognise what to do with) typical files in web development like HTML, CSS, JS, unix files and images.

Feel free to comment with the ideal features you'd like in a PHP IDE! I think this is perhaps one area we can learn a lot from software such as Microsofts IDE's.