Honestly, I've used Zend and I'm trialing NuSphere PhpED and Komodo IDE and I find them far superior to Zend. Zend has the debugger, but in Vista it never worked for me. The CGI would keep crashing out on me every time I went into ZendCore or ZendPlatform. While using the IDE, it hogged some of my resources (though, that could just be a fluke). Anyway, Zend tended to lag a bit because it was java based (much like Eclipse).
NuSphere is one I really really like. It has some flaws, and takes a slight getting used to, but it's really really good. Lots of people who use Zend end up switching to NuSphere once they try it. I can now understand why. It's a better UI (in my opinion) and works really well. It's not java based, so it runs faster on my machine, and does what I need. Since I have my own Apache server, I don't use the debug stuff, so I can't attest to that.
Komodo IDE is really good too. Their 4.0 release is good. I only have a few interface issues (like adding projects is weird) and I don't like that they don't integrate with SVN (at least not that I've seen).
I will say this though, sometimes it's best to shell out the $200 - $300 for an IDE. I'm not ecstatic that I spent that much money on Zend; however, my trials for NuSphere and Komodo are coming to a close, so I may find myself going back until my license expires.
Each company (Zend, NuSphere, ActiveState) offers a 14 to 30 day trial of their software. Just download it and test it. Trust me, you'll find one you like.
Note: Zend does not have a money-back guarantee. That's what the trial is for.
I'm sure I just confused you, but I hope it helps you make a semi-informed decision.
