I have Koni FSD's and Eibach's on my A3 FWD - 18" wheels with 225/40/18 (previously had 225/45/17 on the old Dotz alloys and 16" OE alloys before them).
(Based on when I had the OE 16" wheels): Ride quality is as close to the smoothness of the OE kit, large potholes will unsettle the suspension however you would be hard pressed to see any loss of ride quality otherwise. Handling is greatly improved, not as good as having coilovers etc but much better than what the OE equipment offers.
(Based on the current 18" BBS's and 17" Dotz alloys): Again, ride quality is very good, very slightly less forgiving on large bumps and potholes but this may also have something to do with the profile of the tyres / offset etc.
The FSD setup does 'stiffen up' when you steer sharply - almost like the shock absorber locks in position stopping it from wallowing. It's a compromise of handling and comfort, Audi should have made them like this from the factory IMO.
If you drive through the twisties on smooth(ish) roads, go for something more tuned to handling, if you do the daily commute on pothole ridden roads (read Warickshire) and your car is the main car used for transporting the family, go for the FSD's.
Just my tuppence worth....