Tried AUH-NRT in F and NRT-AUH in J this April, both 10+hr flights. Both were excellent, in terms of service, meal quality, meal quantity, and seats (despite sitting in older A340-500s). F gets more personalized attention.

There are two major differences I felt in F & J.

1) Meal time: Etihad provides high-level meal service in J, with a la carte dining as well as on demand (sort of), and if a passenger orders a glass of wine the crew would actually bring the whole bottle and let the passenger enjoy wine tasting, which quite adds a lot of extra time during meal service. And if this is done on full flight you basically get very slow meal service from beginning to the end as crews are generally busy running down aisles (my mid-night dinner took 2hrs to finish when I was eager to sleep early...). I personally prefer "everyone gets same course same time" in J for a prompt meal service.

2) Seats: If your height is over 183cm (or 72 inches), you won't be able to stretch out your legs in J.

No I did not get mattress pads on my flight in J... and neither lounge-wear as advertized.