Quantifying the speeds of gods starts to become pretty tricky once their abilities cause them to bend or warp reality, transcend time, and break most of the laws of physics. Both the Dragon Ball Universe and the DC Universe have their power sources when it comes to speed, but which one is superior?
Both universes bring powerful contestants to the competition of which power source allows these heroes to reach such godly heights of speed. After comparing Dragon Ball Super's Ultra Instinct with DC's Speed Force, it's obvious that Goku's mastered Ultra Instinct truly is the ultimate power source.
The Flash's Honed Use of the Speed Force
The Speed Force has proven time and time again that the Flash is the fastest man in the DC Universe. In Superman #709, Flash reveals he can think at the speed of light and can perceive things at an attosecond. Then, in Flash #123 (1961) he displays that he can vibrate himself from across the multiverse, and in Flash the Human Race (2009) he outruns an alien's teleportation.
Recently, however, the Flash (more specifically Barry Allen) was able to exceed his prior limits by tapping into the Speed Force itself. The Flash garners a Super Saiyan-like power-up, gaining a bright yellow aura and an immense surge originating from a severe emotional toll, the Flash pummels King Cold to the brink of death. It is unknown how fast this version of the Flash can run, but taking the formula created by Quora User Jamie Wilding, The Flash's top speed is approximately 13 trillion times the speed of light.
Goku's Mastered Ultra Instinct
Assuming that power and speed are relative, as evidenced throughout the series, the speed base Goku can travel is roughly around 2,231.1 MPH. Although Dragon Ball Super does not have confirmed canon power levels, speculation from fans has many believing mastering Ultra Instinct pushes Goku's power level to 2.692 Quattuordecillion, which would mean Ultra Instinct Goku has a speed that can reach roughly 2.3211e+47 MPH (or 2.3211 to the tenth exponent 47 times).
Now let's ignore the math and view it from a more tangible perspective. Mastered Ultra Instinct Goku has accomplished feats of rapid reflexes that the Flash hasn't even come close to. In the "Tournament of Power" arc, Jiren is put up against Universe Six's top assassin Hit, who can completely stop time itself. Hit's power of creating a time cage has been utilized many times to completely stop opponents near or approaching faster than light levels of speed dead in their tracks. However, Jiren with his God-like speed can break this time cage barrier and defeat Hit, meaning Jiren's speed can transcend time itself. Once Goku mastered Ultra Instinct and the incredible power that comes with it, Goku can effortlessly maneuver around Jiren and evade all his attacks. Meaning this type of speed simply is unquantifiable, Goku's speed and reflexes are simply 4D and unlimited.
Also, let's not forget what Ultra Instinct truly does to those that utilize it. Those who demonstrate its divine powers are not bogged down by the brain's commands over the body. Instead, Ultra Instinct allows the body to move without thought. Muscles contract before the brain can send a message telling them to contract -- an indication of just how OP Ultra instinct is when mastered in comparison to the Speed Force.