That depends entirely on your needs and feelings.
For PHP on Windows there are 5 big IDEs:Zend Studio (based on Eclipse)
You should try them to find out which is the best for you. Zend Studio is expensive, but worth the money, especially if you use other Zend Projects like Zend Server or the Zend Framework.
I've used Eclipse PDT a long time and Netbeans too. Both very good IDEs.
Now i've switched to PHPStorm which is temporary the best mix between functionality and speed for small money i think.
If you are searching only an editor, the choice is quite bigger. Just search for PHP Editor, you will find hundreds of them.
Which i can recommend is Notepad++
which i use too or vim
if you like keyboard based Editors.
Which i will never recommend is Adobe Dreamweaver. It is very well known and used, but not really user friendly.