Google has stated multiple times that responsive design is preferred.
Statistics show that more Google searches take place on mobile devices than computers in 10 countries suggest there is importance in having a mobile friendly configured website. Responsive Web Design (RWD) is definitely a major part of the future of SEO.
Does Google prefer responsive website design? Short answer – Yes!
Google’s Preference - Responsive design is Google’s recommended design pattern.
Years ago Google began their big push to reduce duplicate and low-quality content. All else being equal, Google prefers site designers support the crawling efficiency of RWD than have many different versions they must indexed.
Recently, August 18, 2015, Google’s John Mueller used a Google+ post to reinforce that, when pushed, Google recommends responsive:
A good way to make it [a site] work in both worlds [mobile & desktop] would be to have a site that uses responsive web-design techniques to adjust to the size of the user’s device/settings.
At SMX West in March 2015, Google’s Gary Illyes denied that responsive design provides a ranking advantage. According to a write-up of the event:
Mobile-responsive sites are ‘easier for Google,’ according to Gary Illyes, but there is no difference in how responsive and m. sites are treated – meaning, there is no ranking advantage to having a responsive site. It simply reduces the chances of errors with setups that are common with m. sites.
With that said, I do think Google’s overall preference is clear: responsive is the way they’d like webmasters to configure their sites. It may not directly improve the SEO of your website, but it will certainly keep it from being worse.