I want to briefly distinguish them first before talking about which one you should study if you are a foreigner.

In my country, there are hundreds of dialects/accents I can observe. It varies from region to region, and two neighboring neighborhoods can already have two different accents. As a Vietnamese, I have not, to be frank, heard all the accents in my region. There are 3 primary dialects in general (Northern, Mid-side and Southern).

North: Easy to listen to and simplify such sounds and consonants (ch/tr; gi / r / d; x / s). In addition, in the Vietnamese language, Northern people can speak and pronounce a maximum of 6 tones (a huge advantage). When you deeply study our language, you will soon learn about tones. Everyone should, therefore, understand what a Northerner is talking about. They use some regional phrases, but this is never an issue. Most northern people really care about the way they speak, even if it may be a bit off-subject, it must be sweet and super polite (this feature is widely known in Vietnam). Therefore, when listening to them, you will also hear pleasant phrases from northern people. Many individuals discover that the Northern accent sounds rough and not as harmonious and elegant as the other two. But for others, it is just a personal opinion merely for comparison, it may be incorrect.

Mid-side: “strong” (as many people have said) and they use tons of regional terms that, if they speak quickly, the other two (sometimes) can not comprehend. Most of them can only pronounce 5 tones in the Vietnamese language since two tones (~ and.) are not differentiated by their accent. On the other hand, several people said that this accent sounds better and more harmonious than the Northern one. Instead, it seems like people sing. If you have a Northern / Southern accent, it is (usually) difficult to connect with a totally Mid-sider. I used to have a trip to Hoi An, and when I spoke to a merchant to buy a handmade statue, I honestly could not understand what he said because, with many regional terms, the way he spoke was too fast. Anyway, it is always good for Vietnamese people to encounter a new accent (we love each other < 3).

South: they use fewer ethnic terms than mid-sided people do, not too hard to listen to and understand. The Southern accent sounds very sweet and harmonious (this is also commonly known as their great advantage). Southerners also have the same “problem” as Mid-siders for cons, they can only pronounce 5 out of 6 tones in Vietnamese.

Southern people are known for the simplicity of your details and Occasionally, you may not hear beautiful and sweet expressions from them.

So, since it is commonly used, I recommend you study Northern or Southern, and all the other individuals will understand what you are saying. You also don’t need to recall a hundred regional phrases that could confuse you. To learn more about the beauty and diversity of Vietnamese accents, I suggest that you try listening and connecting with different people in Vietnam from different regions. That would be really interesting.

* Fun fact: They can sound like Northern people when Southerners and Mid-siders sing out loud. Therefore, when we listen to him / her singing, it’s difficult to recognize where a Vietnamese singer comes from. Next, when a person wants to imitate the accent of other people when we speak normally, it’s kind of impolite; for friends, it may be all right, but it’s never recommended.

Here are some dialect words that in each accent have the same meaning:

  • The bowl: Bát (Northern and  Mid) = chén / tô (Southern)
  • The fork: Dĩa (Northern and Mid) = Nĩa (Southern)
  • The dish: Đĩa (Northern and Mid) = Dĩa (Southern)
  • “No”: không (Northern) = hông (Southern)
  • Hilarious: buồn cười (Northern and Mid) = mắc cười (Southern)
  • Where: Đâu (North and South) = Mô (Mid-side)
  • Where are you doing? (informal): Mày đi đâu vậy (Northern) = Mày đi đâu zậy/ Mày đi đâu đó (Southern) = Mi đi mô rứa (Mid-side)
  • Over there: Ở kia kìa (Northern) = Ở đó đó (Southern) = Ở tê / tê tề (Mid-side)
  • We (informal): bọn tôi / chúng tôi (Northern) = tụi tui / bọn tui (Southern and Mid-side) 
  • Socks: Tất (Northern and Mid-side) = Vớ (Southern) 

Nguồn: https://www.quora.com/Which-Vietnamese-dialect-should-I-learn