What is the best way to store files when using winforms and web?

Question

I have to develop an application (in C#) that has to work with files. The application consists of two versions: a web version and a windows version. Therefore, the files must be stored on a place where both versions can access the files.

In both versions, the files can be edited and new files can be created.

I've been thinking about the following options to store files:

• IIS using WebDav
• Sharepoint
• Using a share and make this share a virtual directory in IIS.

I don't have experience with one of these options and these were the options that came to my mind.

What is in your eyes the best way to store the files?