It looks like the FFG 14 is the non-drver toe (which you will also hear called Z or quadrax). The FFG 16 comes with the driver toe.
I saw some claims that the FFG 14 can be had with the driver toe - but I am not actually seeing any out there.
All other things being equal, I'd take the driver toe. However, I use both toes and both consistently treat me well. The driver locks in a bit more, but is "fussier" in terms of wanting boot by boot adjustment and a tightness check now and again. The non-driver toe is pretty much "auto" everything.
I'm not exactly a ripping skier, but I weigh over 200#s and spend a decent amount of time on my gear. I guess I'd say that the FFG/STH line is basically super solid in terms of anything most of us will use them for. If you really had a need for one variant or the other, you'd likely know it.
The rationale behing binding prices largely eludes me. The bottom line is that the STH (=FFG) line is a solid value among the pack of "no brainer" good bindings IMO.