Which race is the most powerful in the Star Trek Universe?

Q was the obvious answer but I thought of this one also! Except my memory was so fuzzed up that I misremembered the floating Odin head to be a giant cat-head. In retrospect, I wish I was left to my own devices and kept the cat image.

Nitpick, the Dominion is not a race but a faction, like the Federation, headed by the Founders, who are changelings and are a race

12 years later Star Trek Online calls them ‘Undine’, if you consider that canonical.

My vote is for the dark horses, the Breen. Never turn your back on a Breen.

In the category of those stupid floating alien head things there were Cytherians, from the Nth Degree and the more sinister Nagilum which wanted to kill most of the Enterprise crew to find out more about death.

Wait, I thought those were just Swedish meatballs.

Tribbles.

Humans. It is, after all, a fictional Universe written by Humans for Humans.

But, given the parameters of this fictional Universe, I would say the Q-Continuum.
A single unit might not be omnipotent, but the entire race?

The Q, obviously.

Organians (“Thou shalt not fight!”) and Metrons (“It is you who are interfering. We are merely putting a stop to it.”)

Apollo and his lot.

Probably some never before seen or mentioned race called the Rd n’Brry, who probably caused the universe to come to be in the first place. Later supplanted by the J[sup]2[/sup]a’Brms after the timeline fractured.

The Q, although they are not actually omnipotent; the suicidal Q says they are only omnipotent from a human perspective, just as the Federation could convince some stone age tribe that they are omnipotent.

(Yes I know it’s a zombie.)

One of my favorite fan explanations for this is that the Federation is save scumming. They’ve had limited time travel since Kirk’s era - the idea is that whenever true disaster strikes the Federation, Section 31 or some other Federation organization we’ve never seen travels back in time just far enough and subtly manipulates events so that the Federation survives. Just by “chance”.

How about The Traveler in TNG?

Whatever Scotty had in his bottle.