PFS3 has atomic commits. Basically the filesystem will stay valid regardless when the system is powered off / crashes. Obviously you will lose the data that was being written at the time.
SFS uses journal.
FFS does not provide either.
Personally, I'd put my money on journaling. As far as I know the SFS design follows the ideas laid out very eloquently in Dominic Giampaolo's book
"Practical file system design with the Be file system".
The book, which I bought when it was still in print, was very influential for me when I rewrote the FFS from scratch. I considered adding journaling support to the FFS, but decided against it. Even with journaling support, the FFS would have been weighed down by its comparatively poor data structure design.
Still, given a choice, I would feel much more comfortable with a file system for which working recovery and repair software exists, and make backups of the data I care most about.
FFS may be a poor choice in terms of performance, and all too easily end up in validation state, but if the chips are down you can at least scrape the data off the drive, even if you lost all information about your partition layout. Last time I looked, you were in a world of pain if PFS3 or SFS failed you under circumstances in which FFS would still allow you to sift through the embers.
