The most customizable aspect of the user interface your application delivers is the one provided by Salesforce through its highly customizable layout editor that provides the ability to customize the standard user interface pages (including those now delivered via the mobile client Salesforce1) used to list, create, edit, and delete records.
Lightning Experience is the latest user interface experience available for your desktop users. Salesforce Classic or Aloha is the name given to the existing user interface. Its radically different both in appearance and technology. Fortunately, your existing investments in layouts and Visualforce are still compatible. Lightning however does bring with it a more component driven aspect and with it new tools to that allow even greater customization of the overall user experience.
Keep in mind any user experience you deliver that is not leveraging the standard user interface takes added effort on behalf of the developer...