Well, I agree with a_thing on 2 points. First, and most importantly, use something you like. This means trying things until you find one you like. Second, Quanta is a good choice (in my opinion). However, for management of extremely large projects (or lots of projects), you will find it has some issues (such as code completion that is too many layers deep, or from a files that's included in a file that's included in a file...etc).
As far as Eclipse, I like it. However, I do NOT care for the phpeclipse plugin. Instead I would recommend the
PHPIDE plugin (being
worked on by Zend. However, it still lacks ina couple areas (but is DEFINITELY making progress).
My personal favorite is
Zend Studio, but the Pro version will set you back about $300USD.
I think that a lot of it depends on how much coding you do. I code PHP professionally, so saving even small amounts of time makes it worth spending the $300. I actually regularly use: Zend Studio Pro, Macromedia's Studio (Including Dreamweaver), Eclipse with PHPIDE and
Aptana, Quanta, notepad, and VI.
One last note: Zend Studio and Eclipse are both Cross-Platform (Java based apps that run on Windows, Linux, and MAC). If you develop on different platforms, consistency is nice.