You need to store the internal application settings and you don't need anyone except you to change these settings (for example, developer name, copyright, critical system setting)

You should choose storing of settings in Global asax file (Method 1).

Application settings, which don't need to be frequently changed. Application users can't change these setting, however you need to allow application administrator changing these settings.

You should choose the storing of your setting in Web.config file (Method 2).

To reduce system resources related to file-based operation you can combine this method with using Application and Session objects.

Any changeable application settings if you don't have database installed.

Application settings, which changes very often, and application settings, which have to be changeable by application users.

You should choose the storing application settings in database.

To reduce the number of requests to database you can combine this method with using Cache and Session objects.