You might want to pose the question in the ANA and JAL forums for better feedback. I am not certain but think ANA restricts availability of Premium Economy seats to their members. I know little about JL except their Y is reputed to be among the stingiest in terms of legroom.

Unless you can for certain buy into Premium Economy, I'd suggest considering UA with a cash buy-up to Economy Plus. Less-then-stellar service but definitely more legroom than most in Y.