I flew LX J several times and I think it's ok. BUT......... yesterday I have flown OS J for the first time. WOW! I did FRA-VIE-JFK and Im still shocked. Service and catering (specially on longhaul) are OUTSTANDING and by far the best european or american J class I've ever experienced. I flew FRA-VIE on a 321 and VIE-JFK on a old but "fresh" 767 with the new J seats.
No doubt, choose OS. ^