As a business class passenger/AA plat, you are entitled to any oneworld business class lounge at NRT as long as your connecting flight is operated by an oneworld carrier. In general, in terms of food, drinks and service, Sakura Lounge is the best option given it is JAL's home base but could get crowded during peak hours. And there are multiple Sakura Lounges too and I usually stick to the one in the Main Building. You might want to check out the AC too if you want some quiet time. Below is an excellent thread about different options at NRT.

http://www.flyertalk.com/forum/jal-m...ght=NRT+lounge