I have a similar question: deciding between TK vs LX in J from SIN-SFO (using UA miles).

I flew a lot on LX (in both J & F) until 3 years ago and thought their J product was competent but not great. (Not sure if things have changed much in the past 3 years.)

I have not flow TK long haul before, but I love their J lounge in IST. For the SIN-IST, J configuration is 2-2-2 on A330-300, while for IST-SFO, it's 2-3-2 on 777-300ER, so as others have pointed out, a slight risk of middle seat (two of us are traveling).

Are TK's J seats better? I think TK's catering should be better. What about their wine and champagne selection? I'd think TK service should be warmer and more attentive than LX?