I keep being tempted by the flexibility of the mirror-layouts of btrfs and bcachefs, I have so many old disks that are smaller than my main disks but still a useful amount of space. But ZFS is just so mature and reliable, and the newer contenders seem to still fight with such serious bugs... it's very hard to convince myself to jump over.
The ZFS ecosystem also has some really mature snapshot-based backup system that both snapshot the local disk and can do send/recv to copy to backup disks locally or remotely... and clean up old snapshots. So I'd be signing up to replace that as well.