I loosely follow these guidelines:
- Web Forms/SQLDataSource- Quick and dirty app for internal use to show reporting or some other such data.
- MVC- Simple to complex business logic for a core product.
- MVC/REST Web Services/jQuery- HTML/Whatever type of client RIA's (when user experience reigns supreme).
- Flash/Flex RIA- Useful when an extremely rich client is needed (think multimedia manipulation here).
There are a lot of gaps in this list of course but that just represents how complicated a question it is.
