"Until there is a new ‘official’ update to the mobile guidelines, Google are completely leaving it up to you, but that reply from John Mueller hints that they favour the ‘one URL approach’ of responsive web design – using media queries to serve different versions of the same site."
"When doing web design, it's critical to test how your page looks under different screen resolutions. Since the mobile web is exploding fast, you have to test against the mobile devices too. Resize is a Safari Extension that to make the process dead easy."
"True responsive design is not about catering for specific device pixels — whose dimensions become outdated with every new model that appears on the market — or labelling an experience as ‘this type’ or ‘that type’."
"This is wonderful for everyday mobile users, as the quality of their device screens become sharper and allow them to better experience the finer details of an application. But this creates an interesting challenge — designing for multiple mobile densities."