I don't think the provider is quite as important as the tooling. Both BorgBackup and restic offer important features such as compression, deduplication, and encryption.
But as far as a provider, I have heard good things about Backblaze's B2 service. They have a well known maintenance window, but apart from that their availability is pretty good.
nulloperation wrote
Syncthing is a bit like Dropbox except free / libre and decentralized.