The service very likely will be similarly bad/grumpy/unhelpful as normally on AA. The food is very similar (just somewhat bigger plates and a little nicer setup in F).
The main difference is the seat: really flat with reasonable privacy and space and nobody to climb over/climbing over you. Travelling alone I can sleep fairly well in AA F for several hours, but in J usually don't sleep well. I would spend the extra miles. If you travel with your partner you are close enough on the middle seats to talk, but holding hands is difficult.