I think I've tried every PHP-compatable editor out there, but I always come back to GWDsoft's GTEdit. It's just what I need, not too much stuff I won't use like debugging built in, but not light on high-end features like macros and reg-ex search and replace, either.
IMO the dedicated PHP editors out there are pretty crappy. The only one I haven't used is Zend's, and I'm guessing that'd be the best of the bunch. I tried NUsphere's PHPEd for about a day and found it had too many annoying quirks to be used full-time. Plus the fact that it tried to run its own server was rediculous. About the only feature I liked from that was the built-in MySQL and FTP clients.
Edit: I just tried Zend Studio. I remember why I didn't want to try it, it's written in Java and the interface is rather bulky. It too is very quirky. I hate that, with auto-indent on, it'll do this kind of spacing
function blah()
{
<tab>blah;
}
But if I turn auto-indent off, it won't move me to the same starting position for the next line, it'll do
function blah()
{
blah;<enter>
blah;
}
Where the two "blah"s should be aligned, and I'll have to re-space everything. But other than that it's so handy having all the matching functions/objects/properties/methods show up in a drop-down as you're typing, kinda like Visual Basic. I dunno, I guess if I could find a way around the annoying spacing thing I'd be in business.