Google Drive is a file storage and synchronization service. This service allows users to store files in the cloud, share files, and edit documents, spreadsheets, and presentations with collaborators. You will receive 15GB of free storage to start.
Microsoft OneDrive is a file hosting service that allows users to sync files and later access them from a web browser or mobile device. If you are a very heavy Microsoft Office user, this would be the service to check out.
Dropbox offers simple yet full-featured file sync services. It is one of the oldest file services offered with quite a few integrations to third party cloud providers. Dropbox is offered on all operating systems, Windows, Mac, Linux and mobile operating systems, iOS and Android. This is what sets dropbox apart from Google Drive and Microsoft OneDrive.
Not to be confused with Dropbox Box.com, it is more of an enterprise file storage solution as there are greater user access controls. Additionally, there is a large app store where other applications integrate seemlessly with Box.com services.