I personally believe that apache on windows is still a better solution to develop PHP. Reasons:
- much more documentation about the interaction between PHP and apache (for example url rewriting, proxying, etc...)
- apache is the de-facto standard for PHP, so if you plan to deploy to apache later, you will face less potential problems due to platform differences (also regarding the rare subtle bugs which can plague ported software)
- I find it easier to get meaningful error messages out of apache than from IIS
I try to install the same PHP and Apache versions I will be deploying to, so the chances to have differences is minimal...