I use wide angle through telephotos. (Mamiya 6x7 not Hassie 6x6) so the angle of view is slightly different. Having said that, I think that if you have a 150, going to a 180 has very little difference in the angle of view. The 250 would be a better pick. However, I wouldn't swap one for the other. You'll miss too many shots that the 150 is good for. Is it economical for you to have both the 150 and 250?

Also, you didn't mention what other lenses you have. That could help make a decision.

(edited for clarity)