Start with your prototype and possibly wireframes and then the correct template should jump out at you.
If this does not work for you, then:
- If your app looks like ‘Contacts’, use Navigation-Based Application.
- If you’re writing a game (or something that looks like one), then OpenGL.
If you’re writing something like ‘Calendar’, then use Tab Bar App.
In iPhone Development Quick Start, from Apple, you have a brief description of each:
- Navigation-Based Application. An application that presents data hierarchically, using multiple screens. The Contacts application is an example of a navigation-based application.
- OpenGL ES Application. An application that uses an OpenGL ES–based view to present images or animation.
- Tab Bar Application. An application that presents a radio interface that lets the user choose from several screens. The Clock application is an example of a tab bar application.
- Utility Application. An application that implements a main view and lets the user access a flipside view to perform simple customizations. The Stocks application is an example of a utility application.
- View-Based Application. An application that uses a single view to implement its user interface.
- Window-Based Application. This template serves as a starting point for any application, containing an application delegate and a window. Use this template when you want to implement your own view hierarchy.