To my personal insight, in medium format, a focal shutter should be preferred above the curtain shutter.
In this format, a curtain shutter is more stressed as it must cover and travel over a wider and longer distance, so the mechanical construction has to be more resistant and thus heavier and complex (and even slow), and perhaps needing more 'maintenance'.
Also, by changing a lens, the shutter is changed too, in contrary, a curtain shutter stays in the camera body and has to do the 'work' all the time.
I have to admit never used a MF camera with a curtain shutter so this is only an assumption...