This is my process for developing themes for Wordpress at the moment. I've come to this process because I want to deliver a clean theme while using the power of Gulp for Sass parsing and code/image optimization.
Vagrant for running Wordpress
I don't like to flood my computer with all kinds of tools for different kinds of languages all the time. PHP is one of them that I don't want to think about. Vagrant is a great solution to this. Everything you need for your Wordpress (Like PHP, MySQL etc.) you can get in a Vagrant machine.
With the help of PuPHPet I've made this Vagrant setup for my Wordpress development: