All three. Mostly the 75mm. The 50mm would be next, and the 150mm taking the tail end. Don't use the 150mm that much, but it is nice to have especially for landscapes.
I am not sure there is a correct answer to this question. Before the Mamiya 6, what did you use and what focal lengths did you perfer? I like taking pictures of people and I find the 75mm a very natural focal length - I am not a headshot fan and perfer to relate the person to their environment. I find the 50mm emphasizes the environment too much for my taste.