What's the ordering of 6 realms of rebirth?
The Pali scriptures say:

Mendicants, there are five destinations. What five? Hell, the animal
realm, the ghost realm, humanity and the gods. Nirayo, tiracchānayoni,
pettivisayo, manussā, devā—
AN 9.68
And what is the diversity in kamma? There is kamma to be experienced
in hell, kamma to be experienced in the realm of common animals, kamma
to be experienced in the realm of the hungry shades, kamma to be
experienced in the human world, kamma to be experienced in the world
of the devas. This is called the diversity in kamma.
AN 6.63

Other examples of the above ordering are here.
Therefore, the ordering of the five realms in descending order is:

Gods
Humans
Ghosts
Animals
Hell

However, it appears one sutta, from thousands, namely, Iti 93, includes a separate asura realm and places asura below hungry ghosts.

Being unaware of these three fires, humankind (pajā = people) delights in personal
existence.
Unfree from the bonds of Māra They swell the ranks of hell, existence
in the animal realm, asura-demons and the sphere of ghosts.
Iti 93

Therefore, based on Iti 93, the descending order is:

Deva gods
Humans
Hungry ghosts
Asura gods
Animals
Hell