What do you mean with "digital"?
Analog mode is the one to be used when the application is hard to access with a GUI test automation tool. This depends on the programming language of your application, the kinds of controls and the WinRunner add-ins you have installed/loaded.
In context mode WinRunner "sees" the controls of the application and doesn't need coordinates and bitmap comparisons to perform actions on the application. This makes GUI automation more robust to changes of the application.
Why don't you use context mode? Can you tell us more about the type of your application?