I don't know what's best, but I use bamboo sushi mats. They *do* get mouldy though. You can view this either as an advantage or disadvantage. I do natural rind cheeses and so the sushi mats build up a colony of the flora that's on the cheese. For me that's fine. But if you were trying to age it and keep it super clean, I think a plastic mat or stainless steel rack would be better. For just drying, I don't think it makes any difference at all. Just use what you've got (or what's cheapest). Sushi mats are $1 a piece here and they are eco-friendly, so it's kind of a no-brainer for me. In other places in the world it might be a different story.