I haven't really flown JAL, but I have flown with their Okinawa-based subsidary, Japan TransOcean Air(JTA), I found them to be mediocre, but it's been a few years ago.
I flew the same route with ANA's subsidary, Air Nippon and I found it to be a great flight considering how short it was- 30 minutes with really nice FAs, on-demand beverage service, music, a newspaper in English(it was a regional flight)
I've flown with ANA between Osaka Kansai and Okinawa, when I started flying with them 5 years ago, I was really impressed with them. Back then, they had a nice box meal but my last flight which was a few months ago didn't have food service. The crews were very nice, though.
Now that I have redeemed my WorldPerks miles, I would definitely want to try a Japanese airline from the US to Japan, especially with Northwest's lack of service on such a long flight.
Northwest Airlines - Some People Just Know How to Fly