Seems to be a lot of differing opinions on this. I get that having something between the two can offer less squeaking, some noise abatement and depending on material - a vapor barrier which I may or may not need.
Waxed paper? Paper with tar-infused? Some Tyvek-like material? Nothing?
Help would be greatly appreciated. Some professionals I've talked to seem like they're just trying to upsell me on the latest/greatest Microban-infused super layer stuff. Which leaves me with a wide variety of answers.