So in a recent symfony-zone article about “the best Symfony IDE: PHPEdit“, the author recommended using PHPEdit. Problem is PHPEdit doesn’t have a Mac OS X version according to their requirements page as of this date.
So for now using Zend Studio or BBEdit is probably your best bet. Haven’t tried Netbeans, but at least one developer I know still uses it. Of course you could just use vi if all else fails.
One last thing, Zend Studio probably won’t ever have any first party support for symfony being that Zend Studio’s parent company has their own framework; so I would’t hold my breath for that.