I wasn't sure what you were talking about regarding the different materials. I checked out Liberator's site to see what the difference was. It seems that either polyester or nylon is used for the inner waterproof cover. I have pieces with polyester and pieces with nylon and have not noticed any difference. Since it's the inner cover, it shouldn't affect the function in any way.
I would just pick the shape you like and not put too much consideration into the inner cover material.
When I saw this thread I thought you were going to ask about microfiber vs microsuede. These materials are used for the outer covers. Microfiber is used in most of the shapes. However, microsuede is used in the Jaz. I love this material because it does not attract lint. I wish the larger pieces were made out of it.