1. The Arrowverse's Flash
The Flash was an instant hit for The CW when it premiered back in 2014, showcasing Barry Allen and his abilities off to a whole new legion of fans - fans who clearly liked what they saw as the show remained on the air for nine seasons. Over the course of that show's run, Barry experienced just about every emotion you could possibly feel, and it constantly drove him to be the best version of himself. It's safe to say he accomplished that.
This version of The Flash had it all; incredible speed, the ability to travel through time, throw lightning, phase in and out of solid objects, and heart. So much heart. In many ways, that might have been his greatest weapon, for the man who became the Paragon of Love was capable of inspiring hope in so many people, teaching all of them how to be their own hero.
But in terms of physical abilities, the thing that sets the Arrowverse's Flash apart from his predecessors is experience - and the amount of it. There used to be a running joke throughout the first three seasons about how the Fastest Man Alive literally wasn't the fastest man on the show, as he always had to contend with other evil speedsters. But he always did contend with them, growing from the experience and advancing his own abilities in the process.
By the time the series ended in 2023, Barry was the Fastest Man Alive and had been so for many years. He was a battle-tested warrior worthy of the title as Central City's hero, and from his innate ability to overcome the odds, to the fact that he literally phased a nuclear explosion, he is by far the most powerful Flash of all time.
The fact that the Reverse-Flash couldn't even touch him in the season 7 finale says all you need to know about how fast Barry got before the end of the show.