UFS is reliable and resilient?! Did I miss something? ;-)
The only protections these so called 'legacy filesystems' provide is against loss of DRAM buffer in the storage device. They use journaling or soft-updates or similar solution to protect against inconsistencies in the filesystem metadata after a crash or unclean shutdown. But they do not provide any other protection. All data on UFS is at the mercy of bad sectors and corruption can occur without you ever knowing about it. The metadata is also not protected at all, allowing silent corruption to occur. When using backups, this corruption could spread to your backup medium and provide a false sense of data security.
I would agree with vermaden; always use ZFS unless you really can't, for example when dealing with 128MiB RAM on embedded systems. But generally, ZFS is the first reliable filesystem available to us mortals. Once each platform has its own next-generation filesystem (Btrfs on Linux, ReFS on Microsoft) everyone would want the kind of protection these next-generation filesystems provide and we would frown upon anything less that belongs to a different era.