I flew Vietnam airlines a few years ago in business.
I wrote a trip report here:
Vietnam Airlines HKG-LHR in J
Overall, my experience on-board was very good. There were a few niggles such as the lounges aren't the greatest and the meal on the HKG-SGN sector being not so nice. But for the prices they charge, I was extremely happy.
I've also flown Royal Brunei in economy short-haul. I was unimpressed.