I've lived in both. In BKK for a week right now getting a new visa for VN, and the traffic and noise and road user etiquette is light years ahead of the selfish, homocidal clowns on Vietnamese roads.
Almost everything is better in Thailand - food, weather, air quality, people, infrastructure, vacation destinations, etc etc.
Working in VN is painful - so much corruption and hoop jumping. Only to be treated like <deleted> (and cheated) by your employer. The students are, for the most part, alright.
HCMC and Hanoi are big, noisy, polluted, and in comparison to BKK, bland and backwards. The coastal cities are ok-ish, beaches ok-ish. Some nice natural scenery, if you survive the roads to get to these places.
VN is 15-20 years behing Thailand. And it is still a communist/socialist country, with pig-headed nationalism ever loitering.
It's like a poor version of China, with mediocre food, sh1tty infrastructure, low pay, and no option to settle long-term, if you were foolish enough to make that choice.
On the upside, for every a$$clown there, there is a decent person, the COL is low, and there is some decent natural scenery.
I'm noping out of VN in the next 6-12 months. Too many better places/countries to see and do. And I just can't handle the noise and near death I face every day as a road user.