Although I’ve used Dropbox over the years, I never fully trusted it for documents that were too personal or private in nature. A few high profile compromises later made me accept those gut feelings were correct.
On the other hand… iCloud document syncing has always been a bit of a gong show. The Apple iWorks suite had intermittent issues where documents on the Mini would fail to open or otherwise be out of sync. Dropbox certainly had the reliability advantage.
Dropbox was eventually relegated to only accommodating my 1Password synchronization. With 1Password for Teams I ended up dropping Dropbox entirely.
Fast forward to macOS Sierra. Document created by the iWorks suite seem to be syncing pretty reliably these days. I recently picked up a shiny new MacBook Pro (touch-bar) but find myself going back to my aging 2010 Mini for no other reason than it’s where a ton of my files are stashed.
Sierra has been encouraging me to place my Documents and Desktop folder into iCloud. Maybe this would actually be a decent idea? Ultimately it’s something that Apple will need to get right if they haven’t accomplished this feature already. Going to a particular machine or relying on local storage is starting to feel pretty archaic.