As from the 21st April 2015, Google introduced changes to their search algorithms in favour of mobile sites. If your website isn't 'mobile friendly' then the chances are it will now appear lower down the page rank - read our blog for more.
The decision to go with an adaptive or responsive website, or a mobile app varies depending on business needs, budget and website goals. Sitecore enables the entire mobile experience from start to finish from collecting and understanding data about your mobile customer to delivering personalised, relevant content to them wherever they are.
Sitecore's whitepaper 'From Mobile to multi-channel' looks at the different types of mobile designs offering scenarios for each approach. It explains how Sitecore Adaptive Design allows websites to include key elements of responsive website design while enabling marketers to engage customers in multi channel conversations.