Should I use a cloud service to back up my mac?

USB is the link. Two reliable forms are TimeMachine and CarbonCopyCloner ($39, bombich.com). TM can pull individual files on a very active system. CCC makes an exact copy of even the boot sectors, best run on a relatively quiet (but still active) system ... I use it at end of day to maintain a bootable clone.

Using both methods covers you very well.

USB. A Cloud service is not a backup scheme, it provides file synchronization.