A mobile ergonomic web design outlines any design which presents on mobile devices correctly. Hence, you may need 2 versions, including for desktops. Although you can manage 2 such separate entities, it’ll become taxing in terms of time and cost.
A responsive web design, however, displays on all devices or screen sizes. This offers universal support for all users. It’s effective to handle just one site.
At VOCSO, we use responsive design for new websites rather than mobile design as we believe that these provide a synchronous experience. It’s also more affordable, convenient, and future-proof/supportive than other approaches.