I'd make ILA or Apollo your top two choices. They're both CELTA training centres and so will effectively carry on your development pretty well. For what it's worth, you're probably more likely to get adult classes at Apollo, but you may have to teach in partnership schools (go into public schools and teach large classes of very low level students). I also worked for Language Link for a period, although they didn't have enough classes to offer full time positions (that may be different in Hanoi). I enjoyed working there, but they didn't have any of the same professional development focus as ILA or Apollo (again that may be different in Hanoi).
The best school with the best pay is probably RMIT or The British Council, although you'd be very lucky to get a job at either of those without at least a couple of years experience first.
VUS are a big chain and I've known people who've worked there, including a few people who worked for both them and ILA. The consensus seems to be that they're far less demanding than ILA or Apollo. The courses are taught in tandem with a Vietnamese teacher, who focuses on grammar and reading, while you focus on speaking and listening. Preparation demands are minimal, and pay is about the same, or possibly a tiny bit better. Put simply, if you're looking to make as much money as possible with as little effort as possible, then they're a good choice, but they're probably not going to help your development as a teacher, and they won't look as good on your CV should you eventually want to teach somewhere like RMIT or the British Council.
Cleverlearn is another big school. From what I hear, they don't have the best reputation or pay, but they are pretty successful and could probably offer a full time schedule fairly quickly.
There are plenty of smaller schools around the city too, but their quality and professionalism is massively varied.
If you did your CELTA at ILA btw, then they're the obvious choice, because you get a $750 relocation allowance.
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