I haven't flown TK long haul but I have tried the TK IST lounge and was in the LX ZRH lounge last month. I would say that the LX lounge is comfortable but definitely not amazing. They have some very average hot food cooked to order and a nice outdoor balcony but overall I would rate it as only good, whereas the TK lounge is excellent.

LX longhaul in J is decent, better than average, but again, not amazing. The cabin is very dense. I recently flew United longhaul in J and AA longhaul in J and I would rate AA >> LX >> UA, although the AA flight was empty which probably helped.

I very much doubt that after flying LX one way, that you will regret choosing a different airline to fly back home. There is nothing spectacular about LX. That said, if I was on my own, I would choose LX both ways due to TK not having single seats. Sitting by a stranger is not a worthwhile J experience.