Depends, I've flown with them and other carriers and have found SQ to be pretty reasonable. Some compare them to Qatar. Qatar has a reputation for changing aircraft and some class passengers getting a lower level of hard product that they paid for.
SQ is consistent with their levels of service which puts them ahead of some other carriers IMHO.
I've flown on China Air and found it to be very good. Emirates, well take your chances and if there is an issue try getting a positive result from them.
Thai used to be good but we all know what's happened with them unfortunately.