My choice would be Swiss.

Between LH and UA - it's a tough choice. On one hand, I feel that LH is more reliable when it's not on strike and I feel better cared for on LH (service wise, IRROPS, phone agents, etc). Food is about as bad on both. But LH became very unreliable because of labor issues and unexpected strikes. So in my view, LH = UA.

Several people mentioned TK as superior to LX/LH/UA. I disagree. While TK has great food and IST lounge, I personally would avoid TK at all costs:

1. TK safety and pilot training concerns: AMS crash did not teach them a lesson -- KTM could be nearly as bad, other major mishaps, questionable safety culture, corruption. In addition, Turkey does not make accident reports public, so how much we we do not know?
2. Really really bad IRROPS handling and clueless phone agents.
3. Unstable situation in Turkey.