When Google Drive was announced, I strongly expected that Dropbox would die soon. I was wrong! They are not only still with us, but have nearly doubled in size. They are quite simply the best around. For example, even though they have promised it repeatedly, Google Drive is still not available on Linux. Dropbox is much easier to use that Google Drive as well. Oh, and Dropbox has local syncing so you don't pull mulitiple copies over your Internet connection.
When you make a Google Chrome Packaged App, Google Drive is a natural place to sync to. However, Dropbox makes this process so easy, surely you'll allow syncing there as well. And Dropbox + FirefoxOS is a natural pairing as well.
Dropbox Blows Up the Box, Connecting Every App, File, and Device
Thinking Outside The Dropbox: The Cloud Company Straps On Its Platform Shoes
Dropbox - Datastore API tutorial