Bottom line: If the same content is being served on the desktop and mobile websites, use responsive Web design to maintain the same URL structures and display optimal layouts based on screen size.

FORBES: How to Dial Up Mobile SEO

The next frontier in the evolving One Web approach is building on responsive design techniques to develop websites that are truly adaptive.

FORBES: The Future Of The Web: The Case For Responsive Design

If content serving is dynamic depending on desktop or mobile requests, use responsive Web design to handle different content serving using the same URL structure.

FORBES: How to Dial Up Mobile SEO