The SMC Pentax-M 1.7 50mm is more different from the other two. It 's smaller and takes 49mm filter. The Promater and Vivitar, using 52mm filter, are very similar. I believe that they were made by the same manufacture. Looking through the front elements, I see that the lens coating colors are obviously various among them. The Pentax has more blue, and the Vivitar shows less colored.
With each lens at f1.7, I shot three images below. The top 3 came through the Pentax, the middle 3 generated by the Promaster, and the bottom 3 were the Vivitar's. With the enlarged image in a picture viewer program, I rank them in the order Pentax, Promaster and Vivitar from the best to 3nd.
What is your ranking?
More details on the Promaster and Vivitar 1.7 can be found in my another post.