As of now, I'd say:
1.) Broly
2.) Freeza
3.) Gohan
4.) Oob
Broly has made the largest leap in power in the shortest amount of time, by far. In like 2 hours, he went from being weaker than base Vegeta, to forcing even SSB Gogeta to use his most powerful attack just to drop him... And not only was that the first real fighting/training Broly had ever done, but there was never any indication that he plateaued -- he just kept getting more powerful the entire time(regardless of the 'damage' he took.)
It's hard to say who has more potential between Freeza and Gohan, as they can both make HUGE gains with minimal training. That said, Gohan's major boosts almost exclusively rely on "rage-amp" moments, wherein he becomes super-duper powerful at the time... But then inevitably slacks off again and loses most of the progress he makes.
Freeza, on the other hand, can achieve massive gains by training for relatively short periods of time(as we've seen with his Golden and Black forms), and then just sit on his ass for decades and never weaken.
We've only seen a glimpse of Oob's potential so far, but I fully expect him to get the "most powerful" title one of these days... He ain't there quite yet, though.
The scenes on Beerus planet in Super Hero had Goku and Vegeta go back to calmness, with Vegeta realizing that calmness was part of what made Jiren so strong, though they were just sparring in their normal forms.
Makes me curious how the new Broly will develop as a fighter. They were trying to teach him that lesson of calmness too, but he let a rage moment slip which led to him having to sit out and then watching the mentioned Goku and Vegeta spar.
Being calm is not necessarily having to always fight in normal form. They can still use the powered up super saiyan states, but normal form is the starting point of achieving that fighting calmness, I guess.
Broly also might be like Hulk in a sense... Where he's more powerful unleashed and raging, than he is calm and controlled.
Point him at a target and just let him cut loose.
Yeah, a full decade of training is a long time.
But Freeza still went from being a bit above SSB-level, to casually one-shotting Gas+MUI Goku+UE Vegeta. Even though he had a decade to get that powerful, that is still a massive boost.
Freeza went from being weaker than he was during the Namek saga, to SSB-level, with 4 months of mediocre training. When has Goku ever increased his power by that many orders of magnitude in such a short period of time on his own?
But yeah, obviously Broly's growth in the movie absolutely eclipses anything else in the franchise.
Never let anyone else define you. Don't be a jerk just to be a jerk, but if you are expressing your true inner feelings and beliefs, or at least trying to express that inner child, and everyone gets pissed off about it, never NEVER apologize for it. Let them think what they want, let them define you in their narrow little minds while they suppress every last piece of them just to keep a friend that never liked them for themselves in the first place.