What is the best cloud backup service?
Backblaze is the best pure backup for one computer: truly unlimited, one fixed price, zero configuration. IDrive is the best all-rounder for multiple devices under one plan, and Acronis the power option that combines image backup with security features.
Real backup services (as opposed to sync drives like Dropbox) exist for one scenario: your machine dies, is stolen, or gets encrypted, and you get everything back. Backblaze nails the essentials with radical simplicity: install, forget, and every file on the computer plus connected external drives is continuously backed up, unlimited, with version history. One subscription covers one computer, and the restore-by-mail option (they ship you a drive) solves the big-restore problem.
IDrive wins for households and freelancers with several machines: one plan covers your PCs, Macs, phones, and even NAS devices together, with strong versioning and the Express service that ships you a physical drive to seed the first backup, brilliant on slow connections. Acronis is the enthusiast tier: full disk-image backups (restore Windows itself, not just files) plus bundled anti-malware, at a correspondingly higher price.
Whichever you pick, the decision that matters most is not the brand but the setup: include everything by default, keep versions for at least 30 days, and test a restore once. A backup you have never restored from is a hope, not a plan.