Vietnam has many banks. There is no universally 'best' bank: the choice mainly depends on your situation.
Among the major institutions you will frequently encounter are Vietcombank, BIDV and Techcombank.
For an expatriate, the truly important criteria are rather:
Mobile application
The banking app will likely become your main way to use your account.
Network of branches and ATMs
Particularly useful when you arrive in the country.
Quality of service in English
It can vary significantly depending on the branches.
Bank fees
Look especially at transfers, withdrawals, and cards.
International transfers
A particularly important criterion for someone still having income or savings in Europe.
Currency management
Some banks allow you to hold accounts in different currencies.
Therefore, do not choose a bank solely because it has an ATM next to your residence.