What is the most private cloud storage?
The short answer
Tresorit is the most polished zero-knowledge storage, Swiss and built for business. Proton Drive is the strongest privacy option for individuals and comes from a trusted ecosystem. Filen is the open-source option for a smaller budget. With all three, encryption happens on your device and the provider cannot read anything.
In detail
Private here means zero-knowledge, end-to-end encryption. Your files are encrypted on your device with keys only you hold. The provider stores encrypted data it cannot scan or read. It has nothing readable to hand over. Google, OneDrive and Dropbox encrypt in transit and at rest. They hold the keys themselves. That protects you well against hackers. It does not keep your files private from the provider.
Tresorit has carried the zero-knowledge flag the longest. It works under Swiss law and has excellent apps. Its detailed sharing controls keep working with encryption on. Its pricing fits its business-grade position. Proton Drive brings the same design to consumers at friendlier prices. It carries the trust Proton earned with Mail and VPN, plus the ease of one ecosystem. Filen is the lesser-known contender. Its apps are open source and anyone can verify them.
It is zero-knowledge by default and keenly priced. Sync.com and Internxt complete the category. MEGA uses the same design with the biggest free tier.
Zero-knowledge comes with a few trade-offs. If you lose your password and recovery key, nobody can recover your data. Features like server-side search or photo face grouping are not possible either. These three keep that trade-off as small as it currently gets.