For the purpose of this thread, "more or less powerful" is the degree of ability with which to possess authority, influence, or control over that which exists.
'Most' would obviously mean greatest in quantity, extent, or degree.
But that is ambiguous. So, I might have a great deal of power in one way and someone else a great deal in another way. Both of us may be local maxima, but there may not be a *most* that is above both of us in power.
Authority is a social construct. Influence is a social construct. Control is a mixture of one's ability and one's social connections.
But, for example, a person who is physically strong is able to influence some things, while someone who is eloquent can influence others. Which is more powerful?
Once again, how do you put the power different beings have into an order? How do you say one is more powerful than another unambiguously?
Let's use that which has conscious existence. And preemptively, we will define 'conscious' as having awareness.
In which case I have no idea. Are whales conscious? Probably. And they are probably physically the strongest beings on Earth. But if you want most social influence among humans, we have a completely different question.
On the other hand, like I said, I have no idea whether there are beings on other planets. If there are, I have no idea what their abilities might be and how they would compare to the beings on Earth. Are they more or less powerful then we are? I have no idea.
Also, it is quite possible, even if you define 'powerful' in a precise enough way to define 'more powerful' and 'less powerful' unambiguously and in a way that can be linearly ordered (for every pair, a larger and a smaller can be chosen), there is also the issue that the differences between the top powerful beings are so small that the largest changes from moment to moment.
So, perhaps the most powerful being is some individual in a very strong, very smart, very social species that is able to inspire others to create technology that affects the dynamics of stars. Such an individual would be more powerful than any human.
Do I know if such a being exists? Not at all.