Creality Cloud is a free community and remote-control app for Creality owners: a big model marketplace, free cloud monitoring (Premium is $7.99/mo, and bundled with some new Creality machines), in-app slicing and tight Creality hardware integration. If you have a Creality printer and want free monitoring plus models, it's a great hobbyist pick.
SimplyPrint is print-farm and classroom management that runs any brand. It adds a real print queue, AutoPrint continuous printing, AI failure detection, filament inventory with NFC, a maintenance system, multi-user roles with SSO and a school plan, and it natively runs Bambu, Klipper/Moonraker, Prusa, Marlin, Duet and OctoPrint, with EU + US data centres so you can keep data in-region. For a production fleet, that's the difference.