- Have at least three copies of your data.
- Store the copies on two different media.
- Keep one backup copy offsite.
Personally, I'd recommend:
Copy 1: Your Mac.
Copy 2: A local NAS (my personal choice) or hard disk.
Copy 3: A remote backup, stored on a hard drive in a desk drawer at work, Backblaze, Google Drive, Amazon Cloud Drive or whatever other solution suits your needs.
In terms of software, I personally use rsync + ZFS/BTRFS snapshots (NAS - local, NAS2 - remote) and rclone (cloud). I haven't really used fancy solutions like Attic and Borg due to their need to write dead (i.e. not mountable without a performance penalty) data to local disk or SSH. No affordable storage that I've found offers this (rsync.net offers it but is too expensive).
It's getting to the point where I'm seriously considering buying an LTO6/7 tape drive though...
I'll also add because I haven't seen it elsewhere: verify your backups. A backup is pointless unless you know you can restore it. The best way to test this is by doing it. It should get to the point where you don't fear a restore. It shouldn't be painful. There should be no worry. It should be no more than an inconvenience. When something goes wrong, you don't want there to be even the smallest hint of doubt that there's something wrong with your process.
As such, I strongly recommend having an easily accessible backup. I'd go for a spare HDD sitting in a desk drawer at home before going for cloud backups just so that you can test it frequently.