What is the best way to do indexing in Django 1.11?

Question

Django

I'm making an application on Django 1.11.
Advise whether it is worth creating indexes in the database in a new way:

from django.db import models

class Customer(models.Model):
    first_name = models.CharField(max_length=100)
    last_name = models.CharField(max_length=100)

    class Meta:
        indexes = [
            models.Index(fields=['last_name', 'first_name']),
        ]

or better the old fashioned way, in the model field itself, specifying db_index=True ?
The project will be developed and maintained in the 1.11 branch with a PostgreSQL base.