In general I'd like to understand which templates to use when, when I'm making new iPhone apps. Could anyone offer some guidelines, tips, rules-of-thumb?

Also, how much should I agonize over this? If I start off with the wrong one, can I add the missing pieces manually, is it hard?

For reference here are the choices I'm seeing:

* Navigation-Based Application
* OpenGL ES Application
* Tab Bar Application
* Utility Application
* View-Based Application
* Window-Based Application