There are pros and cons for both web forms and MVC. But you don't have to choose. You can use the nuget package for adding MVC to a web forms application. You just have to start with web forms and then it will incorporate the MVC. That way you can have the best of both worlds depending on what your needs are.
Here is the link to that nuget package from Scott Hanselman.
If you are just looking to do a CMS then you should definitely use Orchard
