Dropbox has started limiting connected devices to 3 on their free accounts. Dropbox has had a few security problems in recent memory. These items have recently overcome Dropbox pros which include: peer to peer syncing, efficient block level syncing.
Read a few articles the best of which is https://startupstash.com/dropbox-alternatives/
Sync.com if you want to keep your data in Canada/North America (My choice)
pCloud winner for most free data at 10Gb
Google Drive for photos as they are essentially unlimited but no privacy protection here
NextCloud if you need to keep your data onsite. Installs on VmWare or Raspberry Pi.
I recommend keeping 1 backup of user data in the cloud. Duplicati2 is free and versatile and heavily encrypts your data.