I would rate the JL lounge in NRT as the overall best place for relaxing and enjoying yourself before your onwards flight...

The AA lounge is spacious and well lit and seems definitely catering to a business audience with ample supply of power points for laptops.
The unique thing about the AA lounge in NRT is that it actually has printers you can use! (thanks to the very friendly lounge attendants at JL who rang around to find which OW lounge had a printer I could use ^ ) As I blurrily recall, they use some web service to submit your print jobs and then you enter some code on the actual printer and then out it pops.
I remember thinking at the time that if they have a suitable timeout on the print jobs that you could even print before you even get to the airport and pick it up on your way through to the plane