Of the materials that you listed, Silicone. While I like Silicone, I think Glass is actually better, or at least I tend to prefer it. Also, Acetal, which is what the Aneros products are made of is nice as far as plastics go. For good prostate stimulation, as with gspot stimulation, hard materials are often much more effective. One negative that I have for Silicone is that it can be hard to wash silicone dildos so that they are absolutely free of any odor that comes from the inevitable turdlet getting on the toy. Glass, Metal and Ceramic are all much much easier to clean. Yes Silicone may be technically nonporous, but it is a lot harder to get fully clean without boiling it or bleaching it than glass, metal or ceramic.