I think it might help if you tell us about your budget. All Hasselblad telephotos are quite good, some better than others in some respect.
The 120/5,6 (old version) and 120/4 are very, very good lenses. However, they are very sharp and can be rather short fort head and shoulder portraits. This really depends on personal taste. I think portraits made with them have a more 3-dimensional look because you are closer to the subject.
The 150/4 is a nice all around telephoto. Older versions can be a bargain. It is also very good, though not as crisp as the 120mm. The look is not as "clinical" as that of the 120mm. Sharp and contrasty nonetheless.
The 180/4 is another lens renowned for its sharpness and high contrast. Considered as one of the best lenses in the Hasselblad-lineup. Rather expensive, as it was introduced in the early 90s and is one of the newer lenses. As the 120mm, some consider it even too sharp for portraiture.
The 250/5,6 is another lens that can be had for cheap. It is quite long, so portraits tend to look flatter than with the other telephotos. It is not as sharp as the others, but this is no drawback for portraiture I think. Depends on taste again. Personally, I don´t like it that much because it is rather dark and slow (5,6) and too long for handheld use.
Then there is the 160mm Tessar. Some like it a lot because it is light and balances well with the camera. Others regard is as inferior to the other telephotos. I don´t know how much truth is in there. It was introduced in the late 90s as a budget lens.
A 32mm Extension tube might serve you well!
