There's no "best" IDE, only better and worse ones.
Right now I'm trying to settle in with Aptana. It has a lot of cruft that I don't want, like "Jaxer" doodads all over the place. It's reasonably fast, but chokes on large files when syntax highliting is on. I have not been able to figure out how to set up PHP debugging. Three good things about Aptana: easy plugin installations, very fast and intuitive Subversion plugins, ligning fast file search.
I tried Eclipse PDT and Zend for Eclipse, but they have nightmare levels of interface cruft. Installing plugins is a living horror of version mismatches and cryptic error messages.
I also use Komodo (they bought us licenses at work). Komodo has a very intuitive interface, but is ridiculously slow, chokes on medium sized files with syntax highlighting. File search is intuitive, but rather slow. Subversion integration is not that great - slow and buggy. If not for slowness, I would have probably stuck with Komodo, especially for the debugger.
