Personally, I find the J seats on the A380 pretty good (I am 5'10), though the F seats are a bit wider and you can get more legroom - for someone who is tall (> 6'2"), they may find that they have to bend their legs a bit while sleeping in J on the A380. Another thing that I find good about J on the A380, is that you can be siting really close to your better half, especially in the EF seats - you can't be that close in the suites.

If you've never flown EK F on the A380, I would say try it one way just for experiencing the suites and the showers. I don't find the food (except for caviar) and wine on board in F all that great and any better than J (in fact, it includes the J menu as well so you know that EK doesn't differentiate between J and F food anyway) and prefer to eat in the lounges, but there are several here who simply love the on board catering. YMMV.