So I know this is an old thread but recently I flew LX Y and I figured I would do a quick comparison. Just so people are aware this is comparing TK Y on the A330 and B777 with the LX A340.

Lounges: I had access to the F lounge in ZRH and when I was in IST the lounge was under construction with no lounge alternative for *G. If comparing a Senator lounge and the new TK lounge maybe my answer would be different.
Edge: LX

Boarding: LX boards with relative order. F,C and *G and then others. TK boarded everyone at once so it was a free for all. Also JNB-IST is an extension of CPT-JNB-IST so a lot of overhead space was gone even though I boarded early.
Edge: LX

Seat: Tk's seat was good. I was comfortable and looked after as a *G. I received bulkhead seats. LX the seat was ok but the head flaps were very used and very flimsy.
Edge: TK

IFE: TK had many choices and new releases. LX had new releases but a little limited selection.
Edge: TK

Food: LX's meal was fine and no complaints. TK's food is the best meal I have had in Y and I fly a lot a lot of Y.
Edge: TK

Operations: LX was on time and no complaints. TK from JNB was delayed 12 hours due to a volcanic eruption. Understandable however every other middle eastern and european flight went out that night. My guess is because of the delay as others were also so delayed an hour or 2, the flight crew timed out due to the flight from CPT-JNB. No hotel was offered or anything. I tried to get put on another carrier and was denied. I was told to sleep in the airport in JNB. No thank you.
Edge: LX

So in the end I would choose TK over LX and would be ok with my choice as long as operations were on normal. In an IRROPS situation LX might be better maybe not.