Ah! Definitely not using Dropbox app to do the syncing for me automatically. Again, too much magic for something too important. I can't be guaranteed that the Dropbox app maybe somehow loses authentication and silently stops syncing, or maybe I edit a photo on iPhone and its filename is unchanged in the filysystem and it doesn't get synced over, or anything similarly weird and technical goes wrong.

Maybe I'm being paranoid but all I want is a perfect and completely transparent guarantee that I have a complete snapshot of my most important files. I'm willing to do the little manual work for it.