We use ShareFile for upload and download of PST files. During email migrations we find ShareFile is secure and easy to use for moving these files from users to email servers. ShareFile is used by project engineers as well as customer engineers.
SharePoint serves a different purpose (organizing and finding content) and the 250 MB file size limitation ruled out its use. Dropbox lacks a security model. FTP is difficult and time consuming to set up.
ShareFile is well suited for organizations that want to share files in a secure manner. Organizations not concerned with security could do with cheaper alternatives. The service is easy to set up and use. It's helpful to have some idea of how you want to organize files and folders based on your security and sharing needs.