In choosing between SQ and TG, I'd go with TG. Overall SQ is probably superior in Y but TG has more legroom and on the LAX-BKK TG uses a A345 which is a very nice plane and has a very decent AVOD system. Also many if not most BKK-Australia routes I believe are now using new B772's which also have more legroom and nice AVOD. TG wins out for me due to the more generous legroom. If that's not so important for you then SQ would probably be your choice due to better service and a shorter distance.