An adaptive design (or dynamic design) identifies the type of device and then serves the appropriate site to the user. Essentially there are three different sites, a desktop, mobile and a tablet site with only content and resources specifically designed for each type of device downloaded at any one time.
The table below summarises the pros and cons of the three options for mobile friendly websites. Also see responsive.
From a user experience perspective an adaptive design is probably the best solution as content can be tailored to the individual device type. You also maintain a single URL which is better for SEO and the load speed should be fast. However, these benefits have to be considered against the additional costs.
Conversion marketing – Glossary of Conversion Marketing.
Over 300 tools reviewed – Digital Marketing Toolbox.