A long time BBEdit user, I bit the bullet and (mostly) switched to Zend Studio back in November 2005. I was frustrated by Zend Studio's clunky Subversion handling, but within a few weeks was willing to put up with that for Zend Studio's great debugging environment and intimate knowledge of PHP that helps speed coding along on a line-by-line basis.
The switch to an Intel Mac broke Zend Studio's great debugger. Whoops! There went at least half of why I was using Zend Studio in the first place. Enter
Komodo Pro. Komodo Pro 3 has supported Intel Macs for months. (Still no word from Zend on this issue.) Its debugging environment is based on the robust Xdebug extension.
Komodo Pro lets me work the way I want to, with the tools (and versions of those tools) I want to use. Zend Studio, on the other hand, does not.