80mm and 250mm is better since it is a 3:1 image change rather than a 2:1 image change. I do not do portraits generally, the 150mm lens is my least used lens.
I think 250mm would be too long for many situations, plus it's a stop slower, both of which are of relevance for shooting hand-held without camera shake.
My advice? Get the 180mm for a long option. It is optically superior to either the 150 or 250, and focuses closer thereby allowing a tightly framed headshot without the use of extension tubes or close up filters. Some people complain that it is too front heavy, but that issue is exaggerated IMO and I certainly don't find it to be a problem. The 120 Makro-Planar can also be a good portrait lens, but is not as good for tight headshots as the 180 because the perspective is then less flattering.
Eventually you will probably want the 50mm as well for city shots.