Originally Posted by
johnnysd
citiAA personal,business and citi Amex 400k miles
You are only using AA miles? Then none of the 'China' airlines are on option.
If you are going to SGN, the only potential airlines would be CX, AY, JL, S7 and possibly MH as they are a future OW airline.
Realistically, your options are CX, JL and MH. Given your desire to not have a long flight in a non-fully flat bed JL might not work (a flight from NRT-SGN is almost 6 hours, with no bed).
CX has a great first class, and their J also has fully-flat seats.
So look into CX and MH. There are lots of trip reports on those, especially CX.