How to choose secure cloud storage
The encryption question comes first
The biggest divide in cloud storage is who can read your files. Most mainstream services encrypt data at rest, which protects it if their disks are stolen but still lets the provider (and anyone who compels them) access your files. End-to-end encrypted services hold only ciphertext: the provider cannot read your data, but you carry the responsibility, because losing your key means losing your files.
Neither model is universally right. End-to-end is the honest choice for sensitive documents; a mainstream provider with convenient sharing and recovery may be better for everyday files you would rather not lose to a forgotten password. Decide by what you are storing, not by which sounds more secure.
The factors people underweight
Sharing and collaboration quietly undermine security: a file shared by a public link is only as private as that link. Check how a service handles link expiry and permissions before you rely on it. Jurisdiction matters at the margins too, affecting who can compel access.
Above all, plan your exit before you enter. The service that is easiest to leave — bulk export, standard file formats, no proprietary lock-in — is the one you can safely commit to, because you are never trapped by a price rise or a policy change.