I'm a fan of pure silicone. No odor, no taste, and easy to clean and sterilize. I'm ok with plastic, and I'm considering getting a cyberskin or something for camming my guy (oral mainly, MAYBE vaginal). But when silicone's an option, I prefer it.
Glass and metal are also enjoyable. I think I personally prefer them for anal, though, not vaginal. I don't know why.