Dropbox.com has only a business solution if you want more storage Mega.nz does not seem to support two-factor authentication for high security
Looking for alternatives which support Ubuntu clients
Box.com and Sync.com do not have any :(
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It only takes a minute to sign up.Sign up to join this community
Dropbox, https://www.dropbox.com/install-linux, Install the appropriate package if you want to use Dropbox on your Linux Desktop.
Google Drive, Insync, https://www.insynchq.com/, Insync extends Drive's web functionality to your desktop by integrating tightly with Windows, Mac and Linux so you can get work done.
Rclone, http://rclone.org, Rclone is a command line tool for synchronizing files and folders to multiple cloud storages (either from your machine or from one cloud storage to another). It supports Dropbox, Google Drive, Amazon S3, Amazon Drive, Microsoft One Drive, Yandex Disk, and more.
RcloneBrowser, https://mmozeiko.github.io/RcloneBrowser/, Simple cross platfrom GUI for rclone command line tool. Supports Windows, macOS and GNU/Linux.