I know F0RBIDDEN has the 1200F and seems to like it w/ Reaper - he'll probably chime in, but being in the market for a Firewire interface myself, I would personally get the 400F in a hot second if it had ADAT i/o...
...but since it doesn't, I really don't wanna spend $750 on an interface that will only give me a maximum of 10 inputs. So Fireface 400 it is for me!