Even though we covered this a couple times, most recently in September, saying responsive design is not a ranking signal, I wanted to cite a different Googler who said Google does not rank responsive design sites better than other mobile configures web sites that comply with their guidelines.
Google's Zineb Ait Bahajji said in a Google Webmaster Help thread clearly and directly:
We do not rank responsive web design sites better than sites using other configurations (separate site for mobile or dynamic serving).
Yes, she also points out that this is written clearly and directly in their developer recommendations:
Google does not favor any particular URL format as long as the page(s) and all page assets are accessible to all Googlebot user-agents.
But both Google and Bing prefer responsive design over others for a few reasons. But mostly because it requires less resources and the link signals are clearer.
Zineb said the reason Google prefers it is because "it's easier to maintain, it's future-friendly and we see less configuration errors with RWD (faulty redirects or bad user-agent detection for instance)."
Forum discussion at Google Webmaster Help.
