esl advice

You can probably get by and find employment with either course.  Hundreds of teachers have taken only online courses of questionable quality.  The real question is which course will give you the best training for your sake.  Assuming you are not going back to school for a full blown teaching certificate in EFL, the best course is surely the CELTA.  It is the only one that I know of that has a significant in class practicum element. 

You can take the CELTA in Britain but it may actually better to take it in Hanoi or HCMC.  The reasons are 1) price, 2) 30 days to familiarize yourself with life in Vietnam, 3) your practicums will be with Vietnamese speakers whose problems are different than speakers of other languages, and 4) you can start applying for jobs before you finish the class.

Just to add to Thigv's post, if you do the course in VN, the school will line you up with a fairly decent job upon completion.

I have considered a celta course for a long time but have been put off by people who tell me I simply won't need it to find work there. Plus it has no young learner specific training. I would much prefer to do a full time 4 week course in VN itself. Although I can only find courses tesol/celta and there 1000 dollars upwards. Does anyone know of any 4 week courses that are a little cheaper?