I've been coding in PHP/MySQL/HTML/CSS/JS for many years. Dreamweaver has done a lot of good things in its evolution. The CS4 offering is good, but still lacks those things that are absolutely needed for professionals...real time code checking, code completion etc. These are absolutes.
PHPed is an OK offering, but only available in Windows. Despite its claims, it is NOT stable on Mac or Linux platforms.
Zend and Aptana are virtually the same thing. Both are Eclips-PDT based products, except Aptana is more full featured. Zend has been very unresponsive to its customers in not including simple things like word wrap, for instance. Aptana Studio 1.5 was outstanding with its own PHP plugin, but is no longer available since they adopted the unfinished, raw PDT.
NetBeans is absolutely the BEST PHP platform, but has a downside in running away with memory..at least on the Mac it does (this could be an issue with the Java VM however). But it DOES provide the best set of features...and its free.
Aptana 1.5 is my choice at the moment, but since it's not being enhanced anymore, I'm looking for a new IDE of choice. So far that's been NetBeans. I'm hoping that they will eventually fix the memory leaks.