the processing time in Vietnam is estimated to 5 working days if the application is complete (longer if they need to ask you to submit additional documentation).
The processing time in Cambodia is 10 working days (not incl. the day of submission). The processing time resets if they need to ask you to submit additional documentation.
According to their own information, the estimated processing time at The Thai consulate in HCMC is 5 working days* if the application is complete and the Thai consulate don't see the need to ask for additional documentation.
*I've seen reports that the visa process in HCMC have taken a bit longer lately though (10 working days seems more accurate).
In my opinion, the estimated processing time of 5 working days at the Thai Embassy in Hanoi seems pretty accurate. I'd personally choose Hanoi if the processing time's of great essence.
I'd say the Thai Embassy in Hanoi, Vietnam is one of the quickest atm. Their estimated processing time is 5 working days if the application is complete. If they request additional documents the processing time resets.
Even if you are not planning a vacation you should consider that it may well take 2 weeks (or even longer).
Anonym deltagare I've seen this reply from the Thai embassy in Hanoi, when a person asked if their employer could sponsor them. I haven't seen any posts of a DTV-application actually being approved in such case though...
Thailand has 2 diplomatic representative offices in Vietnam - Thai Embassy in Hanoi and Thai Consulate in HCMC.
You can stay ANYWHERE in Vietnam when you apply. If in the north, choose Hanoi. If in the south, choose HCMC.
They reserves the right to call you in for an interview, so you just need to be prepared to travel to the city of application if asked for an interview.