Hi,
Whilst I agree the JAL F lounge is the best, the main terminal F lounge is closed for renovation currently;
Narita Airport Lounge Closure
and there are mixed reports about non JAL pax being denied entry due to capacity.
The AA and QF J lounges are pretty good for J lounges and I felt the AA one was a very good AA lounge ( compared to some of the US ones prior to being renovated)
Regards
TBS