This has to be settled because this two teams has on more than one ocassion shown to be more powerful than the other. So, let's discuss who is the most powerful group. 
 
I'll post some points in favor of each team. 

Cosmic Cubes: 
 
- In the first story arc with a Cosmic Cube, it was shown Thanos taking over the universe with the CC. In a sense, he took over Eternity. 
- Beyonder and Molecule Man, both half-Cosmic Cubes, entered in battle and shook over the universe. 
- Dr. Doom in Secret Wars seemingly used the power of a Cosmic Cube to take over the power of Galactus. 
- During Infinity Wars, Magus used the power of five Cosmic Cubes to put Eternity into a coma and potentially could kill him. 
- During Infinity Crusade, Goddes used 30 Cosmic Cubes and created the Cosmic Egg. One of the most powerful objects in the Multiverse. 
- This is the peak of the iceberg, when the Guardians of the Galaxy went to the future, The Badoon used the last remaining Cosmic Cube to enslave dozens of Celestials and create the Celestial Engine. 
 
Celestials: 
 
- In the come of the Third Host of Celestials to the Earth, Odin along with Zeus and Vishnu attacked with a blast so powerful it could destroy the galaxy. The blast did little damage to Arishem. 
- Odin then attacked them with the Asgardian Destroyer. The Destroyer is an enchanted armor that greatly increases the power of the user. Arishem was able to goe toe-to-toe with the Destroyer Armor and then the entire Host overwhelmed it. 
- Kubik and Beyonder admitted that a single Celestial surpasses them in power. This says a lot. Apparently this have been retconned due to the "peak of the iceberg". 
- Thor at full power with a Godblast did nothing to Arishem. Then he used the same thing against Exitar and the only thing he did was to get his ass handed to him by Exitar. 
- Scathan, a Celestial from the future judged against Protege, who at the time had the power of the Living Tribunal and defeated him. 
 
That's everything I can think of now, so debate.

People on this site need to remember one basic rule.  The extra-dimension is infinitely vast compared to Eternity. Think of the planet Earth as Eternity (one universe). The entire space around that Earth is the extra-dimension, and that can go forever. The Comsic Cubes transfer and manipulate extra-dimensional energies. So depending on the size of consciousness of the cube because all cubes are different, the more powerful the affect.

If you can find out what characters originate from the extra-dimensional space, you will know who are the most powerful entities in Marvel Comics.

Your saying Cosmic Cubes are almost as powerful as Abstracts?

@___Living_Tribunal_22__:

I think when in the hands of a person with great imagination and willpower, a cosmic cube has the potential to be powerful on a universal or possibly even multiversal scale .

As the Shaper himself claimed , a cube's greatest limitation is its inability to dream/imagine on its own

Fast one more with LT avatar

I liked the original Beyonder.

There was no reason to retcon him.

@thegodkiller: Sounds a lot more like the ultimate nullifier in the hands of Galactus,or Reed Richards.Someone with the intellect to use it to it`s full potential,in their hands it is a multi-versal weapon,far beyond the cosmic cube.I don`t want to here about self imposed taboo`s.How could anyone trust Mephisto,Thanos gave him a non-functioning cube,he`s no dummy.Mephisto wanted to have the same powers in the real world,that he enjoys in hell.

im pretty sure celestials are higher on the cosmic food chain but i have heard otherwise recently

Depends on which Celestial and which Cosmic Cube.

The strongest Celestial is stronger than the strongest Cosmic Cube.

However, the average Celestial is weaker then the average Cosmic Cube.

Jmarshmallow

Bump

@thanosii said:

To answer this question definitively, CC is leagues above Celestials, and Thanos has beaten Kosmos in direct combat which says a lot about him, I think, but CC's are above Celestials according to this scan:

That scan is dope, from Guardians of the Galaxy Vol. 2 Issue #16.