Viettel
Viettel is one of the major operators in the country.
It is often an interesting choice for someone who wishes to travel regularly outside the major metropolitan areas.
VinaPhone
VinaPhone belongs to the VNPT group and is also one of the large national networks.
MobiFone
MobiFone is the other major historical player and offers SIM and eSIM as well as solutions specifically designed for foreigners arriving in Vietnam.
For someone who is truly settling down, it is better to choose a large operator rather than buying an anonymous tourist SIM from any reseller.