Disclaimer: I'm not affiliated with Roots, just a satisfied user.
In response to several recent questions on the topic of starter themes, the following are my thoughts on what I believe is the best starter theme available today, along with a heads-up on an upcoming resource that may help you in the near future.
Recommendations for starter themes come up quite often in AWP, and my first instinct is to recommend Roots' Sage starter theme (https://roots.io/sage/), but to be honest, it's not for everyone. I feel like I always have to attach the caveat concerning the prerequisites: Node.js, gulp, Bower, CSS preprocessing, build processes, etc. I often see advanced devs discouraging others from trying Sage if they're not 100% up to date on all of these tools. Don't let that scare you.