Dodgeman is right, I have used both 15# roofing felts and rosin paper. The felt is better at trapping moisture and that is its problem. It is better to have moisture go through the floor to the basement or crawlspace. I have never had a moisture problem, but live in a very dry climate. Rosin paper is somewhat fragile but gives the floor a smooth finish and allows expansion and contraction without any sticking and popping and allows moisture to go through. My personal take is that the floors I installed on felt were a little quieter and seem to move less. The most recent floor I did 2-weeks ago over rosin paper.
Since you clarified you are using full dimension wood floor nailed, I think you can go right over the OSB subbloor if joist spacing is 16" OC and not more than 19.2". If your floors are on 24" centers you should consider reinforcing plywood (at least 3/8"). The manufacturers see OSB and plywood, as equivalent and require a minimum 5/8-inch or thicker plywood or 23/32-inch underlayment-grade oriented strand board (OSB), but prefer 3/4". If your OSB subfloor exhibits any flaking or delamination at all (like it was weathered) I would apply the plywood underlayment, otherwise you should be fine.