I've flown both.

Sleeping: AA's seat is a less clastrophobic and a little longer. I found the JAL solo seat comfortable as well and slept well in both. AAs seat swivels into a desk position which can be quite nice if you have work to do. JAL's seat has a side table with quite alot of storage. I'm 6'1" and did not feel in any way confined in the JAL solo seat. Also liked the PJs JAL provided. Just plain more comfortable when on that long of a flight.

Food: No contest. JAL's Waygu beef entree is not to be missed. One of the finest steaks I've ever had. I also loved the ramen snack. Only things AA has going for it is the seafood appetizer and the sundaes.

Service: AAs is wildly inconsistent. AA FAs are at the absolute top of the seniority ladder. Some FAs try to provide professional service and truly care about the product they provide. Others, well, act as if they earned the right to take a load off their feet and relax. I had one incident when I had to get up and track down the attendent as she hadn't appeared in a half hour after I rang the call button. Just didn't car and looked annoyed that I expected her to do something. Not an attitude you should expect in F.

Entertainment: I bring my own, so could not comment.

My suggestion, try both, fly AA F outbound and JL on the return. Then report back with your impressions.