i have used KONI Sport and Bilstein B6 dampers, but not FSD (B6 are exactly the same as B8 except not short-stroke).
i have B6 on my 155. whilst the suspension design is completely different to the 156, i still consider them a little too stiff/hard on the 'compression', and a little too underdamped on 'rebound'...for my tastes. i fitted them for 'something different', to experience Bilsteins.
KONI Sport i've used on many cars, including my current GT. but also my previous 156 TS. both cars with Eibach Pro Kit, and i really, really like them. the Sport are meant to be slightly less 'comfortable' than the FSD, yet i find them very acceptable...for my tastes. given FSD are 'more comfortable' i think they should be great in this regard. but my impression is that they are less firm/sporty/performance-orientated than Sport, so are a compromise biased slightly towards comfort and less towards performance compared with the Sport items. i cannot confirm this though, cos i've never tried FSD.
i think if you are wanting comfort with some added sportiness, FSD is the way to go. i would expect Bilstein to be a bit stiffer (i've also heard similar opinions from other people, with various types of cars).
if you wish to save a bit of money compared with FSD, and would be happy with slightly more sportiness and slightly less comfort, consider KONI Sport.