Should I come in on a 3 or 6 month visa ?

Do you intend on getting a work permit and stay for a few years?

Hi and welcome,
To the best of my knowledge, Vietnam doesn't give a 6-month tourist visa. You can get a 3-month one and later do a visa run for 3 more months.
You can, however, get a 6-month business visa if you want.
Cheers!

Hi Kiana,

As senwl mentions above "To the best of my knowledge, Vietnam doesn't give a 6-month tourist visa. " Also, as far as I know, that is true.

If you have never been to Vietnam, it's probably better to just come on a 3-month tourist visa, which in my experience can be extended in-country another three months. That may not always be the case though, depending on your nationality and the current policies,

That would give you 3 to 6 months to try out VN and see if you like it before investing in getting a longer more expensive business visa.  There's a lot of hype regarding teaching in VN right now, but actually it can be quite challenging, especially living in the big cities with millions of people and motorbikes, pollution, etc.

If you have been here before and are certain you will stay longer, then it might be worth it to look into arranging a business visa through an agent.

Just got in Saturday and got a 1 year tourist visa, can't post sites on here, but do some research and the VOA letter will costs no more than $25 but stamp fee will be higher for a 6 month visa.

I paid $135 for my year long visa stamp fee on Saturday.

Hi. I got a six month multiple entry tourist visa. I have to leave the country after 90 days so will fly off to Hong Kong on a Visa run. When I get back, will ride the train from Hanoi to Ho Chi Minh City in June.

The 1 yr (or 6 month) multi-entry tourist visa with a cap of 90 days for each stay is available to the US citizens only. 
OP is from South Africa. At best she can get a 3 month multi-entry tourist visa.