Malak and Maul are both renowned saber masters, Sith Lords, and horrific combatants.
Malak's edge include his more esoteric Force usage, his home-court advantage (he is actively getting a buff on the Star Forge), his longer saber blade (Check the in-game model; it's longer than normal), and his impressive size and reach. He's also pretty quick and Force Drain/Force Stun are two Force powers he has which Maul has never canonically shown resistance to, nor necessarily even encountered.
That being said, Maul is a dangerous assassin who's ability to work both offense and defense is highly valued, and he is not a pushover in any sense.
I think in pure sabers, Maul might even eventually wear Malak down or capitalize on his recklessness. Malak does not have a cool head whatsoever. Given the nebulous method of measuring their styles against each other (or in the case of some, just writing off Malak entirely because "NO FEATS"
, Maul's cooler head and more methodical style prevail here.
In terms of Force usage, Maul is kind of overwhelmed. Even if he can resist Force stun (which begs for proof, but all the same), Force Drain, Whirlwind, etc. are all powers Malak has displayed, and while he's probably not on Revan-levels of Force mastery, he is still the best of the best among the Sith Empire attacking the Republic at this time. Also, Maul does not have a history of killing people using the Force (IIRC, I may have forgotten something), and Malak does, which is another point in his favor.
Lastly, given the Star Forge amp, which made Revan (a clear superior to Malak) work hard for victory (Drew K, KotOR writer) this might skew things even more in his favor. Especially in a Force confrontation.
Feel free to checkout my Revan Respect Thread (It's kinda long, lol. Dedicated a summer on it) , for I can guarantee you Revan won't be "stomping" Maul, however he is Maul's superior by a fair distance nevertheless.