Which stochastic screen

To make matters more complicated, there are of course different "stochastic screens" (or aquatint screens). In the end it will be up to you and your work on which you will decide. Stochastic screen are not cheap, certainly not the big ones. Handel your screens with care, they get scratched easily .

 Click for larger picture (Takach Press)

Resolution;

Fine: the fine pattern will produce a softer toned image, it produces a lower contrast.
Medium; the all around screen, average contrast. This is the one I use, certainly the best screen to start with.
Coarse; for high contrast results, use this one.
Most screens on offer seem to be around 80% density. You could get an aquatint screen (80%-1800dpi) produced, if you can still find a good imagesetter service. Some people print their own on an inkjet printer, but I have no clue if the quality of their work is up to standards.

You will have to do a test run for each screen you want to use. The screens come in different sizes.
There is more than one place selling the screens, here are a few:
Takach Press
Precision Digital Negatives
Polymetaal (only medium resolution)
Grafisk Eksperimentarium