"The Ones" were the most powerful force wielders ever.
"The Father" is clearly the most powerful in the force.
"The Father" kept "The Son" and "The Daughter" at bay, and made sure there was balance in the force.
"The Father" also made sure the that Abeloth didn't destroy or ruin the universe.
Entire religions were spawned after "The Ones."
They've also been around the longest going back to 1,000,000 BBY.
In the Star Wars Universe nobody was more powerful in the force than "The Father" as he kept things in order for all that time and had a huge responsibility, without him things would have fell apart.
Since you included "force entity" in your question, this is a clear cut answer.
The Clone Wars "Overlords":
The Father: You cannot imagine what pain it is to have such love for
your children and realize that they could tear the very fabric of our
AS: I don't understand.
The Father: It is only here that I can control them A family in
balance. The light and the dark. Day with night. Destruction replaced
AS: Then why reveal yourselves to us? There are some who would like to
exploit our power. The sith are but one.
The Father: Too much dark or light would be the undoing of life as you
So the guy keeping "life as you understand it" together and holding the force in the balance for over a million years is definitely the most powerful force wielder ever.
Somebody else put the same answer but wasn't definitive, and didn't include quotes or reasons to prove it. I can include more quotes, but clearly The Father is the most powerful force wielder. After him come The Son, The Daughter, and Abeloth. These beings are stronger in the force than multiple Jedi or Sith combined.