Placing two characters of vastly different power levels into combat is simply uninteresting. With that in mind, certain powers are more important than others. None are more important than superspeed.
Take Quicksilver for instance. He could take down the X-Men by himself. I'm not exactly sure just how fast Quicksilver is, but I've seen him illustrated as a blur, so I'm guessing fast. How many characters in the Marvel Universe are fast enough to react to him?
In DC Comics, we have the Flash. He can move at speeds approaching that of light, which according to relativity builds up near infinite mass. Packing that much of a punch, even Superman could be knocked clear off the planet. He can vibrate through walls, move faster than the eye can see, and travels so fast around the globe he might as well be teleporting.
These characters don't only have superfast legs, they have superfast brains, which is the real advantage. Bruce Wayne may be smarter than Barry Allen all speeds being equal, but the rate that the Flash processes information bumps him up to super genius. In his eyes we are all moving in so-mo. How can Batman ever catch him off guard?
Characters like Green ...