The Flash is one of the most important superheroes in DC Comics for many reasons. He's also one of the most powerful. That's not just discussing his speed, either. A lot of other abilities come along with the tremendous power the Flash has at his disposal. Comics being comics, though, he's not the only version.
The multiverse will be explored in the upcoming Flash movie, which is appropriate as it was The Flash who introduced the concept into comic books in "Flash Of Two Worlds," from The Flash #123 in 1961. This seminal story set off decades of other versions of The Flash, some far more powerful than others.
Jay Garrick
Jay Garrick, the original Flash, debuted in Flash Comics #1 in November of 1939. As one of the earliest superheroes in comics, his powers were impressive but not god-like as in later versions. Jay Garrick could run at the speed of sound, which was beyond impressive in 1939, before the jet engine.
He didn't have the benefit of the Speed Force, the energy field that powered later versions of the Flash, but was still one of the fastest and most powerful superheroes of his day.
Avery Ho
Avery Ho gained her superspeed when the Speed Force went haywire. She first appeared in The Flash #3 in 2016 and is very fast. Given how new she is, she may not have reached her top speed yet, but so far she has yet to hit light speed. Many of the fastest Flashes can do that with relative ease.
Avery is distinct in her powers though in that she can actually siphon speed from other people to make herself go faster. This makes her unique amongst the many versions of the Flash, at least for now.
Bart Allen
Bart Allen, who has been at times both Impulse and Flash, can go faster than the speed of light. This gives him an enormous amount of power as he does it through the Speed Force. Moving at this speed, Bart is able to effectively transcend relativity.
He was born in the 30th century, a descendant of Barry Allen, but his molecules were so unstable that he aged rapidly. He was eventually stabilized after coming into the present day, where he's also been a major part of the Young Justice superhero team.
Black Flash
It's hard to imagine anything faster than the speed of light, but the Black Flash is. What makes this terrifying entity so powerful is his ability to catch up to speedsters and essentially reclaim them into the Speed Force. A manifestation of death filtered through the Speed Force itself, he is unimaginably powerful.
Black Flash is himself immortal, making him essentially impossible to defeat. He first appeared in 1998, in The Flash #138, when he came to collect Wally West back into the Speed Force.
Reverse Flash
The Reverse Flash is among the greatest of The Flash's villains. He's also one of the most powerful. Eobard Thawne debuted in The Flash #139 in 1963, and like The Flash himself, has seen a general uptick in his power potential.
In the modern era, he has become the master user of the Negative Speed Force, the inverse version of the natural energy field that gives speedsters their power. He can phase through objects as well as create speed vortices, whirlwinds of such size and speed they're beyond destructive.
Zoom
As with the Flash, there are different versions of the Reverse Flash as well. One of the most powerful is Zoom. Zoom showed up as the primary antagonist to the Wally West version of The Flash, debuting in The Flash Secret Files and Origins #3 2001.
He took his name and costume from the original Reverse Flash but he was even more powerful. He is so fast that he has been able to run across time and space, speeding up or slowing down time at will, granting him power beyond comprehension.
Wally West
Wally West became The Flash after the cataclysmic events of Crisis On Infinite Earths in 1985. Barry Allen died in that crossover, which was recently adapted into the Arrowverse. It's Wally West who first discovers the concept of the Speed Force, and presides over a major expansion in the abilities of The Flash.
He either invented or perfected a number of essential powers associated with The Flash, including the Speed Steal, construct generation, and the ability to enter and exit the Speed Force at will.
Barry Allen
Barry Allen is the current Flash in the comics, as well as the Flash in both the Arrowverse and the DCEU. He is certainly one of the fastest versions of the character and one of the most powerful. Barry can run faster than the speed of light and is a master in all forms of the Speed Force. Greater than that, he actually created the very energy field that gives him his powers.
Wally West was the first to explore the Speed Force, but a retcon in the Flash: Rebirth comic book revealed that it's actually Barry who creates the force with his movements and thus creates the source of power for all his allies and enemies.
Kingdom Come Flash
Even greater in power than Wally West is Wallace West, the Flash from the seminal '90s comic book series Kingdom Come by writer Mark Waid and artist Alex Ross. This version of the character was so fast he was always moving, only able to be perceived as a red blur.
He was actually the amalgamation of several characters merged in the Speed Force, including Wally, Barry Allen, and Jay Garrick. This version of the character also has interdimensional awareness, making him near god-like in his perception of time and space.
The Red Death
The Red Death is one of the most recent versions of The Flash, and in many ways, is the most powerful. Debuting in the Dark Knights: Metal comic book event from 2019, this is a twisted fusion of Batman and The Flash. The Batman decides he simply needs the Speed Force to prevent crime in the world, leading to a version of The Flash that is beyond powerful.
He can form various Bat-gadgets faster than the speed of light, such as batarangs. His most powerful feature is his intellect. The mind of Bruce Wayne combined with the speed of The Flash results in a truly powerful entity.