I’d shoot for the best schedule initially and then review and adjust as you sit back and take stock! Especially important for me would be the flight back to MEL and when back to work etc.

I personally favour TG as they have a bigger fleet than MH. I also have greater faith in the standards of their aircrew and maintenance - although on any given day you can have a bad crew (cabin and/or flightdeck).

THAI’s A350 is a newer aircraft that will beat the A330 for thing like cabin pressure, window size etc. I also prefer TG’s J seat over MH’s.

Finally, BKK is a nicer airport than KUL and since you’d be on TG some decent *A lounges to hop around. Although it has been a few years since I was through KUL.