In case you do not intend to remain in Vietnam for a long term at once, Vietnam 5-year visa is a good choice, as it is valid for up to 5 years and you can remain in Vietnam for up to 6 months each stay.
But 5-year visa is not a good choice if you want to remain in Vietnam for over 6 months as it will put you in a complicated and costly procedure of visa extension. In this case, a TT visa should be the best as it is a good base to apply for a TT temporary residence card in Vietnam which is valid for up to 3 years and its holder is allowed to remain in Vietnam during its validity.
In addition, with a TT TRC (obtained based on Vietnam TT visa), you can open a bank account in Vietnam which holders of a 5-year Vietnam visa cannot do.