I'm hard of hearing, so I don't notice any difference between FF and Dacron. Unless the bow requires Dacron (my Grayling Kodiak Mag), I prefer FF due to a (perceived - I don't have a chrono) increase in speed, longer life and a little extra safety factor if one or more of the strands should get cut.
What really has me shaking my head is people saying the FF is harsh on their fingers. Your fingers never touch the string. If both strings are served to fit the nock, they both feel the same to me.