ZFS is of course the rock-star file system in FreeBSD, with numerous features and new ones frequently coming in, but UFS is also a pretty solid deal which is perfectly usable for a wide number of tasks. Here are some of my favourite UFS features.
#1: UFS is a pretty old file system which has been continually incrementally upgraded though the years. One of its best features is that its memory usage is conservative (compared to ZFS). As an "organic" file system it has evolved with the BSD kernel and both are pretty much tied together and work best with each other.
#2: Soft Updates is an extremely elegant solution to file system consistency and actually the optimal solution in some cases. Consider a database which has its own log (like PostgreSQL and MySQL's InnoDB) - using journalling would simply log everything twice, while soft updates simply passes the data through. In addition to that, soft updates has an interesting property regarding short-lived (e.g. temporary) files: if you create a file, write a small amount of data to it, then delete it all in a short time span, neither data nor metadata from this file will ever touch the disk drive platters. No inode, free space bitmap or directory files will be changed if a file is short lived enough to not be seen by a checkpoint and it's not explicitely fsync-ed.
#3: Soft Updates Journalling was created to get around the few corner cases which Soft Updates alone cannot track. A fsck is sometimes needed when a file system is not unmounted cleanly with Soft Updates alone (and usually happens in the background), but with the addition of journalling, there are much fewer such cases. This feature is not a "log" for data in the sense like ext3/4's log can work or how ZFS works, but a journal of some (not all) operations which need special care and recovery. Consequently, it is very small and efficient.
#4: Snapshots are an integral feature of UFS, and happen on the file system level. By using snapshots before backing up databases, you can be sure that a consistent image of database files is recorded at the point of time where you started the snapshot. If the database is ACID enough, this is all that is needed to ensure a successful backup. ZFS's snapshots are quicker to make and writable (while UFS's are a bit slow and read-only) but if you are doing nightly backups, they could be good enough for many cases.
#5: UFS supports TRIM natively, which allows it to efficiently delete data on SSDs.
#6: UFS has both fragments and blocks, so files less than a block size (usually 32 KiB on recent FreeBSD versions) can be stored in individual fragments (4 KiB on those systems). These sizes are configurable at file system creation, so it is perfectly ok to create a file system which is optimized for storing files less than 1 KiB in size, while having a decent block size of 8 KiB.