I used to use Dropbox extensively, and had my own photo syncing system setup that used Hazel on my computer, and Dropbox on mine and my wife’s phone to colocate our photos into one library. I also used it for it’s file-sharing ability as per normal.
That all changed when I found out how they were circumventing Apple’s security on OSX to get the access they “needed”.
Now, I use iCloud for everything. Photos are synced with iCloud photo library (it’s a minor annoyance that even though we’re setup as a “Family” on iCloud, we can’t share a photo library). There have been instances where it’s taken exception to a group of photos and forgotten they exist. My wedding photos have been lost twice, but luckily I keep offline backups. These aren’t automatic backups (as I would like), but I routinely export copies of photos from the library and into a file (which gets backed up separately). iCloud backing up the Photo Library database doesn’t give me enough confidence, proved by my wedding photos.
All my emails are on iCloud, I’ve always used iCloud, MobileMe, and .Mac before that. It’s been the most dependable email system I’ve encountered. Rumours of the way Google uses email contents on Gmail accounts are worrying.
Love the tab syncing between devices in Safari, that’s very useful. As is clipboard sharing because I use my iPad for dev work, where clipboard management is still clunky. Copying on my laptop, and pasting on the iPad works well.
Calendar sync through iCloud is so-so. My wife seems to have more issues with devices not syncing than I do, but it’s never lost anything. Only errors have been human (deleted the wrong, shared event).
All my music now comes from Apple Music. I archived away my personal library a few years ago, forgot I even had it, and just started fresh. For the amount of music I listen to, Apple Music (or Spotify) is a no brainer.
I’ve started to use iCloud Drive more and more. It’s slowly gained my trust, purely for the ability that I can still use a separate system to create my own backups (Arq uploading to Backblaze B2) because the synced folders are just that; folders. Anything that syncs between devices is notoriously hard to backup automatically because of when things get deleted on one device, and propagates through. This system seems to handle that so far.
I’m about as comfortable with all this data being synced and shared as I’m ever likely to be. Apple have the best track record so far when it comes to privacy, even if cloud services have been their Achilles heel. They’re at a point that they’re easy enough to be worth using, and secure enough (I think) that I’m not worried. If either of those things changed, I’d be gone like a shot.