I would avoid hosting your own server at all costs, it will be anything but easy for non-techies.

Dropbox for Teams and Google Drive are OK, but I find that Google Drive is very confusing to many people. I personally don't think Google Drive has a very good interface and I very much dislike Google Docs.

My recommendation would be Box. It's $15/user per month - so it isn't exactly the cheapest thing out there. But the collaboration tools are phenomenal, and users can store all their documents directly on their machines and upload like Dropbox, great versioning support, and it can be configured to be seamless for those that aren't tech savvy.