I use a stop bath for both paper and film. Stop bath has the amazing ability to halt the development step, and to prevent the formation of dichroic fog that can occur when fixing has begun and development has not stopped. With paper, it can extent the life of the fixer.
For paper, I used citric acid solution as it has no odor.
For film, in the past I used regular indicating stop, but now I an using a buffered stop bath similar to what is described in "The Film Developing Cookbook". This is a solution of acetic acid and sodium acetate. It is supposed to stop very quickly due to a higher acid content, and also has a high dissolved solids content that is supposed to help with swelling of the emulsion.
As far as stop bath with pyro developers go, I found that I could not detect a significant difference between using a stop bath and a water bath with PMK processed films. The only difference I found was that the water bath processed films were slightly higher in density, but I would attribute that difference to the fact that the development was not halted as quickly with the water bath as it was with a stop bath. And the difference in densitites was small. So I use a stop with PMK.