I use the files app with a little modification: The root folder is session-based, so it's possible that every user can have its own "upload-interface".
But Files with an empty folder is a little bit "naked". And if you're new and don't try right mouse-button or don't find the options button on top right, you're helpless...
For a good user experience it would be great to have at least an upload-button (maybe on the top right,too).
Any ideas to realize it?