Don't use the registry: that is decidedly not the right way to do it.
It used to be recommended, but the registry rapidly became bloated, and it gave a lot of problems. So access to the registry has deliberately been made harder, and is very likely to become even harder in future releases to discourage such use.
App.Config is exactly the right place: particularly if there is a chance it may need to be modified, or in a "application data" folder as described here:
Where Should I Store My Data?[
^]
Personally, I use this these days:
Instance Storage - A Simple Way to Share Configuration Data among Applications[
^]