Fay is has a pretty sound, but it's also a bit retro. I think combos with this name could either sound very modern, feminine, and unique, or they could fall into the trap of sounding very dated and stereotypical.
Freya is good on paper, but I'm not sure how I'd like it outside of it being a concept. Again, it's dependent on the combo. If I had to choose between the two, I'd pick
Fay.
My favorite F-name is hard to choose. Right now, it's a dead tie between
Finola and
Francesca.