Nice to see people who know their comics here.
The original Beyonder in secret wars I, was certainly protrayed as being all powerful, above Eternity, Death and Galactus. I don't think the Living tribunial was created yet (have to check).
This was later retconed, in fact he was just one part of a cosmic cube, cosmic cubes are very very powerful, but are below the Celestials who are in one theory servants of Eternity.
In current marvel contunity, the Living Tribunal (LT) is typically considered Top dog. He is in charge of all the multiuniverses, while Eternity is in charge of one universe (616 universe is the name given the main stream Marvel). The LT claims to report to one even higher, often dubbed by fans as "The One above all" (not to be confused with the Celestial with the same name) but we don't know anything about this 'One above all' but most fans assume he is God.
It is said that the LT is truly multi-universal, because there is only one of him in all the multiuniverses, while even cosmic abstracts like Eternity have seperate copies in other universes.
Phoenix Force fans, argue that Pheonix is actually at least equal to LT, and most probably even superior, but that's another argument.
The holder of the infinity gauntlet, has proven to be superior to Eternity, but it's unclear if it gives him even power to defy the living tribunial. There's a scene where the LT orders Adam Warlock to give up the infinity gauntlet, and he does. But depending on how you interprete the conversation he does it because he knows he will lose if he fights or he might win but he doesn't want the universe destroyed in the struggle.
Certainly, after that event, the LT ruled that the infinity gems can never be used together to form the IG, so obviously indidivually, they don't have the power to defy the LT.
In "Marvel the end", Thanos, finds and uses "the Heart of the Universe", comparing it to the infinity gauntlet (which he has held and used), Thanos finds the infinity gauntelet inferior!
He proves it by destroying and absorbing every cosmic entity, even the Living tribunal into him!
I am of the view that the holder of the Heart of the Universe is truly omnipotent
though that is arguable of course.
The cosmic hierarchy goes something like this my opinion
The one above all
Holder of Heart of universe (might be 1 spots lower)
Pheonix force (might be 1 spot higher)/ Living Tribunal
The true beyonders (not to be confused with the original Beyonder who is merely a part of a cosmic cube- The beyonders created the cosmic cubes very little is known about them)
Holder of Infinity gauntlet/ infinity being (might be 1 spot higher)
Eternity(Infinity)/Abraxas
Death/ Lord Chaos/Master Order/Mistress Love/hate etc
Galactus (Galactus has very variable power he is considered equal in importance as Eternity and Death but seems to be much less powerful) - I probably overrate him here.
Inbetweener (servant of Lord Chaos and master order)/The Stranger (4th face of Living tribunal??)
Celestials
Franklin Richards (he is considered one of the Celestials, maybe even more powerful)
Cosmic cubes/Molecule Man
Then there are some things like the Starband which threatens even the LT, the Anmoly who can resist even the power of the Infinity gauntlet... Or Eon/Epoch who powers Quasar...
Earth born highfather dieties like Odin and Zeus are way below on this list.
Magical deities like The Vishanti and the much weaker Dormammu, cytorrak are higher up but probably still below Cosmic cubes level.
Fanboys. Heck wolferine killed Jean grey, so Wolferine is a cosmic entity too.