68 Million username and password hashes have been hacked from Dropbox.  Be sure your password is strong and newer than 2012.  https://www.troyhunt.com/the-dropbox-hack-is-real/

Here's why I've dropped Dropbox:

• Dropbox hacks your machine's security
  http://applehelpwriter.com/2016/08/29/discovering-how-dropbox-hacks-your-mac/ and
  http://applehelpwriter.com/2016/07/28/revealing-dropboxs-dirty-little-security-hack/
  
• They will test software on YOUR machine without your knowledge
  https://sethvargo.com/dropbox-hasnt-learned-their-lession/
  
• Members of their Board of Directors support warrant-less surveillance
  http://www.drop-dropbox.com/
  
• Dropbox alters its behaviour if it detects developer tools installed
  Not true, but I believed it possible, which illustrates the poor opinion I've developed of it
  

For years now I've been using Dropbox.  It's a great cross platform cloud repository.  But I've always encrypted any sensitive files I store there.  I never really trusted it, especially after Condolezza Rice joined their board.

So I'm switching.  There's lots of good options, but here's some notable ones I considered:

• Syncthing - https://syncthing.net/
  
• Seafile - https://www.seafile.com/en/home/
  
• nextCloud - https://nextcloud.com/
  
• Librevault - https://librevault.com/ (only in alpha currently)
  
• hubiC - https://hubic.com/en/offers/
  
• Box - https://www.box.com/
  

I can't recommend Microsoft's OneDrive because a) not cross-platform, and b) each of my Win10 machines all logged into the same account see different contents on OneDrive.

Since I have an always-on NAS running, I went with nextCloud and am running my own server.  It's great!  The mobile client is responsive and clear, and the desktop clients unobtrusive.  Best thing is it's open source, so anyone can review the source code to see exactly why it's behaving a certain way, or compile their own version with their own changes.

I already use Box as well, but only through a web browser.  I have nothing against it, I was just more dependent on Dropbox, and now wanted a server I could control.