There have been plenty of speedsters across the DC Universe, such as the various members of the Flash family, but there are relatively fewer speedsters who appear in the Marvel Universe. That said, Marvel's most naturally gifted speedster, Pietro Maximoff aka Quicksilver, could potentially keep up with DC's Max Mercury, who once shared his moniker.
Here's a breakdown of the two speedsters and who's faster.
Who Is Max Mercury?
Max Mercury first appeared during the Golden Age of Comics as a Quality Comics character. At the time, he went by the name Quicksilver in titles like National Comics and Uncle Sam Quarterly. Little was revealed about the character then , which allowed Mark Waid to largely create an original character from the concept.
Redubbed Max Mercury, the character was reintroduced to the Post-Crisis DC Universe as a former soldier from the 1830s. After witnessing local Native American tribes he'd befriended be slaughtered by his superior officers, Max was enchanted by a shaman with a connection to the Speed-Force.
It's through this connection that Max became a superhero across multiple time periods. He became an ally to Wally West and a mentor to multiple heroes like Jay Garrick and Impulse. After vanishing into the Speed-Force due to the machinations of the Rival, Max briefly returned in The Flash: Rebirth. Max hasn't appeared fully in the post-Flashpoint version of the DC Universe, but is shown to be one of the speedsters Wally West remembers from the Post-Crisis universe.
Who Is Quicksilver?
Pietro Maximoff was originally one of the members of the Brotherhood of Evil Mutants, the henchmen of Magneto in the earliest issues of X-Men. However, alongside his sister Scarlet Witch, Quicksilver ended up joining the Avengers and becoming a hero in his own right -- although he oftentimes butted heads with his nominal teammates. His short temper made him a tense partner in a number of different teams (including X-Factor).
Although he's at times been considered Magneto's son, other retcons have left that a mystery. Quicksilver had a daughter with the Inhuman Crystal and became a consistent ally to the various heroes of the Marvel Universe -- although he has briefly become a villain again at various points, attacking his former allies in the Avengers and proving to be the mastermind behind the events of House of M. Using his superspeed, Quicksilver has been crucial to the survival of the entire Marvel Universe.
Who's the Better Speedster?
Quicksilver has appeared in far more stories than Max Mercury, which means he has more proven feats than the DC speedster. He's fast enough to dismantle machines in seconds, can move across the globe in minutes and is quick enough to dodge lightning. He's one of the fastest beings in the Marvel Universe and capable of some genuinely impressive feats, easily keeping up with universal powerhouses.
However, the DC Universe empowers many speedsters through the otherworldly Speed-Force. It's through this plane that the various versions of the Flash are able to draw on their super speed, granting them a power that's almost unrivaled. As a member of the Flash legacy, Max has been shown moving faster than the speed of light and through the time-stream itself.
His wealth of experience means Max has had the time to even perfect something known as the Zen of Speed, an understanding and understated connection with the Speed-Force which allows the speedster to move without thinking. Jay Garrick considers Max to be a greater speedster than him, telling Wally that the things Max can teach are techniques not even Jay can use. Max is even the one to realize during "The Return of Barry Allen" that the reason Barry hasn't been able to surpass the top speeds of the original Flash is because he's afraid to overshadow his late-mentor.
Max has a deep understanding of his power and the potential it possesses, which might give him the edge over Quicksilver. If Max Mercury can even take the Flash by surprise on occasion, then there's nothing Pietro could do to keep him with.