If you got a chance to book the flight operated by TG on 747 new config (via LHR/FRA/CDG) or 777 - it's the best solution for sure. Thai cabins got very calm ambience (747 on upper deck), service is much more personal than LH-drill style. Also TG new seats gives you much more privacy than front hall on Lufty jumbos.
If you pay for the ticket by your own - Swiss is the cheapest option usually, so the choice will be obvious...
Raf