Here John Carter jumps in to the discussion, "A major disadvantage of iCloud is that it does not allow sharing between users in the way that Dropbox does. However, iCloud has other features that aren’t available in Dropbox. So it becomes prudent to know what iCloud is for and to take advantage of those features in addition to using Dropbox for what it does best.
* My Photo Stream and iCloud Photo Sharing
* Syncing documents and app data
* Mail, Contacts, Calendar, browser data, Reminders, and Notes
* iCloud Keychain
* Find My Device and Find My Friends
* iCloud backup
* Apple TV
* Back to my Mac
And John summarizes, "Some of those features require Mavericks, and some are available in Mountain Lion or Lion."