If you are eligible for E-visa, you should apply this kind of visa. It costs 25 USD and has these features:
- 30 days of stay
- single entry
- Be eligible for 46 countries
- Can enter through 28 ports (included airports, seaports and land borders)
- Apply through Vietnam government website
If you are not eligible for E-visa, you should apply Visa on arrival. It costs from 6 - 50 USD (depend on how long you stay, how many time you enter and which agency you apply with)
- Can stay in Vietnam 1 month, 3 months, or more
- Single or multiple entry
- Be eligible for all countries
- Can enter through 6 international airports
- Apply through Vietnam agency
My recommended agency: Vietnam-evisa.com (it costs 6 USD for approval letter for 1 month single tourist visa. They processing time said that 2 working days, but I received within 1 day)