If you are a professional, use NuSphere's PhpEd. It's the fastest IDE I've seen. It also has everything you would ever want: SVG, FTP, SFTP, Project Management, a world class debugger, very cool and pleasant looks, adaptive GUI, ...... Download a trial version. You will love it. P.S. It may take a few days to get used to it. But once you get used to it, you don't need anything else. With other IDEs, you'd need the IDE itself, an FTP client, a browser and an explorer window. But PhpEd has all that (and more) built in.
My vote goes for notepad if you're a GOOD (experienced) PHP coder. Otherwise : Macromedia Dreamweawer!!!!
Another vote for Notepad ++ here if you are working in Windows. It is truly splendid. I haven't found a great one for Mac yet. TextWrangler is okay but I haven't grown to love it the way I have Notepad ++.
Netbeans - http://www.netbeans.org/features/php/. Hands down better than Zend, Eclipse, or DW. Has built in FTP, or SVN publishing. It's totally free, and is far easier to use than Zend or eclipse.
I like Zend especially the autocomplete and I am using KomodoEdit on my ubuntu you should try that too KomodoEdit is free and support other language such as python, perl and ruby