I am trying to figure out how to create this mottled texture used in the poster below? Looks like a noise filter of some kind. Would I be better using Photoshop or Illustrator for this? I am using the texture in the context of a book, repeating the texture on certain pages.
Well, have you already tried?
Have you tried the Effect>Pixelate>Whatever, or something else in that area of the Effect dropdown? There are some options there.