This kind of use case seems to me like a good fit for ModeShape. Give it a whirl in a proof of concept, and prove it to yourself.
We've not really compared the RESTful and WebDAV APIs, primarily because normally they would be chosen based upon functional requirements. Personally, I prefer the RESTful API because it is more flexible/powerful.
Bear in mind, however, that if you're building this service for others, you may want to consider creating your own RESTful API that exposes your service's functionality. The downside is that it's a bit more work (tho the RESTful service is pretty straightforward, and yours will likely be even more focused), but the upside is that you get to control your API and have it do exactly what you want it to do. We have no plans to break the API, but it is always something we might decide is worth it on major releases.
Thanks for your help.
We started out project in jackrabbit then we met with modeshape. we move fastly to modeshape.