My Installer wants to use Aquabar "B" . I know since I chose him over all the others that I should trust his judgement but, I read from NOFMA that they recommend 15 lb. Asphalt paper as the underlayment between my 3/4" plywood subfloor and my soon to be installed 3/4" unfinished quartersawn white oak. Just wanting to check if anyone really knows that either they are both fine or go with one choice over the other and why? Thanks, floor going in later this week.

Either one will work fine. Keep in mind, those products are NOT moisture barriers. If there is excessive moisture vapor coming from a basement or crawl space, placing either on the subfloor will not stop it. Aquarbar B SUPOSSEDLY has a better ability to stop moisture transfer. The NWFA recommends 15 lb. asphalt saturated felt because it works and is available pretty much everywhere. Aquabar is not available everywhere.