What is the difference between S-Controls and Visualforce in salesforce?

Scontrols:-S-controls have been superseded by Visualforce pages. After March 2010 organizations that have never created s-controls, as well as new organizations, won't be allowed to create them. Existing s-controls will remain unaffected, and can still be edited. We recommend that you move your s-controls to Visualforce. We continue to support the Scontrol object.

Visualforce:-Visualforce is the new force.com technology that lets you create custom user interfaces for your Force.com applications. With Visualforce, you can reuse many of the components found in existing Salesforce interfaces, or create your own. Moreover, the interfaces can also tap into custom business logic. The technique is powerful, easily customized, separates business logic from user interface design, and in most cases eliminates the need for S-Controls. The custom pages can either complement and extend existing pages on Salesforce, or have their own unique look and feel.

The trinity of the existing Force.com platform together with Visualforce and their associated controllers provide a way to construct traditional MVC web applications, albeit hosted on the Force.com platform.

difference between Visualforce and S-control:-

Scontrols get executed in the browser client-side. It is definitely recommended to implement Visualforce pages instead of SControls for user-interface customizations.