I self-hosted a Nextcloud installation and used 2x 4TB drives. The first is full dedicated to the Nextcloud use while the second is rsync-ed to the first every night. Then I deleted my 8 years old Dropbox account. Currently my only cloud provider is iCloud just for the photos, contacts, iwhatever backup.
This is a timely post. I just set up NextCloud myself, to sync my external HDD to my own managed cloud storage service. I've got NextCloud running on a VPS, and linked to a series of storage buckets on Wasabi.
Sometimes all I want is a quick and easy replication of local data to an off site storage facility, and also an easy way to share links with third parties who need access to certain stuff. I am getting tired of storage providers who started off by doing these two things really well, but then decided they wanted to add a ton of bells and whistles that are really of no value to me as a user.
(To be fair, I think Box.Net is the only cloud storage provider I've used over the past decade that still retains their original premise).
It's been a stupid decision at the time of the setup. Now its already there, and any attempt to change it will have to erase the drives, and this is a huge pain in the arse.
I recommend Nextcloud as well. For anyone interested but without self-hosting a server, I've had great experience hooking it up with my Disroot (disroot.org) email account which offers 4gb (free) storage.
Some while back Seafile looked more promising than Nextcloud to me. Never got around to actually using either though. Not sure how things shape up now.