I suggest you use a Platinum SWU and fly Delta in Business class. The trip from LAX to BKK would be 1 connection in NRT and the DL lounges in Tokyo are as nice as Delta has in it's network. KE's A380 from LAX to ICN is a nice way to cross the Pacific, upstairs in the all business class upper deck it is quiet, spacious and the attendants are gracious, but I found the fares to be a little higher than DL.
The DL A330 in business is pretty comfortable. If you take the DL 744 there are full flat business seats.The food service on DL has been upgraded but the service varies depending on the crew.
I just came back yesterday from BKK on DL. No one in the back looked comfortable, EC or regular coach. If it is your choice to sit in economy, then fly the carrier with the best times for journey.