Always use ZFS if you want to use software RAID arrays. And never rely on RAID alone, also use some form of offline backup alongside them, and ideally you should also keep a spare ready to be used automatically in case of failure.
Which is why RAID doesn’t really make sense for small number of disks, only starts working out around 6-8 disks and up. If you only have 2-5 disks you’re much better off setting them up as backup rather than RAID, and only make small arrays if you absolutely must.
Some examples:
You have 2 disks: use 1 live + 1 backup.
3 disks: 1 live + 1 backup + 1 another backup, or 2 in ZFS mirror + 1 backup.
4 disks: 2 mirrored + 1 backup + 1 another backup, or 2 mirrored + 1 standby spare + 1 backup. Do not do RAID with 3 or 4 disks without a standby spare, it makes no sense, and even if you do RAID5 + 1 spare or RAID10 you don’t have backups, the RAID won’t protect against accidental deletions.
5 disks: this is where you can do 3 in parity RAID + 1 spare + 1 backup, or triple RAID1 + 2 backups for ultra safety, or RAID6 without spare + 1 backup (provided you buy another disk as soon as one fails in the RAID6).