There isn't a speedster more powerful than Black Flash, because he is Death for those connected to the Speed Force. Any version of Flash who had a near-death experience, or who died, saw Black Flash at the moment of their demise. However, there is one Flash who actually defeated Black Flash in a fight, Wally West.
In the comics, Barry Allen outran the Black Flash for 20 years (real life and in universe) from Crisis on Infinite Earths to Infinite Crisis. Wally West was much faster than Barry Allen, and so would be able to complete such a feat as well.
Black Flash is a distortion in space that occurs when cursed energy is applied within 0.000001 seconds of a physical hit. When a sorcerer is able to achieve this, their cursed energy flashes black, and the destructive power of their strike is equal to a normal hit to the power of 2.5.
#141” Black Flash is actually faster than Wally. He narrowly escapes death itself by running to the end of time where Black Flash simply evaporates since death has no meaning there. So it would make sense for Black Flash to be the fastest considering it's a physical representation of Death for speedsters.
Doctor Strange is a Master of the Mystic Arts who wields a number of powerful spells and artifacts, making him a dangerous threat. Beating the Flash as simple as Doctor Strange moving the battlefield to another dimension or changing into one of his more powerful forms.
Barry Allen's abilities are relatively straightforward - he can run really quick, at 2,532 mph. Between the Black Widow, a skilled, yet human, fighter, this battle would last less than ten seconds. Barry Allen has proven that non-mutated humans are of little consequence to him.
Weaknesses. Extreme Cold: When exposed to extreme cold, Black Flash's speed is reduced. If it is completely frozen, Black Flash can be more easily shattered to pieces than most.
Time Manipulation: The Black Flash can freeze time in the world around it, only those with extreme levels of superspeed can be attuned to the world being frozen because of the entity. Immortality: As an aspect of death, the Black Flash cannot die by any ordinary means.
And Wally has been definitively and repeatedly stated to be faster and more powerful than Barry—even by Barry himself. That's pretty slow for speedster standards.
While Black Flash was able to overpower Barry Allen and the Scarlet Speedster couldn't escape his chase, there is one thing that keeps him ranked number one on the list of the fastest speedsters on The Flash. Barry Allen is known as the Fastest Man Alive, and that isn't just a cute nickname.
In the comics, Black Flash is basically a Grim Reaper for speedsters, sending them back to Speed Force upon their death. While technically a villain, Black Flash is more of a personification of Death than a mustache-twirling antagonist.
Garrick claims that without the Speed Force, his own power is less than before: like Wally West in the Crisis on Infinite Earths aftermath, he can only run close to the speed of sound. He also states that, as the Speed Force is no longer retarding his aging, his speed is diminishing with time.
He doesn't need a cosmic treadmill to travel through time like Barry once did, and has even outrun death (in the form of the Black Flash) just like his uncle. In the series Flash Forward, it was determined that Wally West is the fastest being in the whole Multiverse.
Savitar was the fastest Speedster we had seen up to season 3. He was so fast that he casually outpaced and toyed with Barry. However, Barry in season 4 was stated to move faster than ANY Speedster ever has.
But Black Adam having ascended to the level of a god puts him on a level that the Flash could only dream of. While it might be some time until fans actually see a race between Teth-Adam and the Scarlet Speedster, the former is convinced he'd absolutely trounce the latter.
Black Flash would win. Zoom's ability is to speed up or slow down his personal “flow of time” relative to that of other persons (including metahuman speedsters) which gives him the ability to act faster than any metahuman speedster.
While it is fairly obvious that the Flash could run circles around Thanos under normal circumstances as his powers make him virtually untouchable, there wouldn't be much the Scarlet Speedster could do if he was around for Thanos' Infinity Snap as there is no way to outrun the god-like power of cosmic chance.
Hurting the Hulk would be hard for the Flash, especially since every missed attack would make the Hulk angrier. However, the Flash can always deploy the infinite mass punch, his most devastating attack. It would be a last resort but it would give the Flash the win.
With his speed, tactical genius, and fighting skills, Red Death was easily one of the deadliest speedsters Barry has ever encountered and a powerful foe for DC's heroes to overcome. Red Death was such a formidable opponent that Barry alone couldn't defeat him in combat.
