There’s no single best...
iCloud isn’t a Mac backup strategy. Single files and manual copies, sure. Not a recoverable system backup, though.
SpiderOak or BackBlaze or ilk, if you want remote. Maybe via Carbon Copy Cloner, or some other client.
Third-party NAS vendors offer storage compatible with Time Machine. FreeNAS, Synology, etc.
Direct attached local storage is the cheapest approach. Big USB disks or RAID arrays.
A Mac with sufficient storage can be used as a Time Machine target, too.
NAS (like Time Capsule) is handy with portables, as the backups happen when on the Wi-Fi, without cabling.
Six to eight terabytes is one hard disk, these days. Not even a big hard disk. Not very much storage.
Consider replicated backups, either two locally, or (better) at two different locations where the Mac roams.
Usual caveat: RAID is (also) not a backup strategy.
Various previous discussions, too. Searching for “Synology” will turn up a few previous.
Practice your restores. So you know it works, and so you can test and document when you aren’t stressed out.