If you have a 200 series camera, I would agree with Peter and recommend the 110/2 -- it is superb, and pretty much all I ever use for portraits on the Hasselblad.
If you don't, I would say go with the 150mm. The 120mm is also a very good lens, and perhaps a better balance to the 180mm in focal length, but if you find the 180mm too crisp, you are likely to find the 120mm too crisp at portrait range as well. The 150mm is also a very sharp lens, but is perhaps not as contrasty as the 180mm. It is also just about right in terms of field of view. You might want to get an extension tube if you want very close portraits though...I think it focuses to 1.4m without the tube, which is around head and shoulders in frame. The 150mm is the classic Hasselblad portrait lens, it tends to be inexpensive, and it would definitely be the first one to try. If it is still too sharp for you, you might go looking for a softar...
