Not the best tread for talk about that, but i will answer.
I tested both programs, and freetrack is a bit more reactive imo, you can turn your head as fast as you can, the view follow exactly in same time.
When, with facetrack the view need a little 1/4 of second for begin to move, in game it's less noticiable, but still.
I found also the traveling a bit smoother.
With a ps3 eye, facetrack locks the refresh at 50fps max, freetrack allow 125fps (for the test i tested both programs at 50fps).
CPU usage is a bit more higher on facetrack : 25-30% (maybe the cause of the latence i experience sometime), freetrack : 1-4 %, with an i5 750 clocked @4ghz.
Beside that, both are great softwares, and a big addition for immersion in simracing, but if you have the possibility to build your own tracking system for the coast of 3 infrared LED, freetrack have some significant advantages imo.