I must confess, I'm more familiar with Canon Fisto than Legends (there are a couple books I am only familiar with, and have not read that include Fisto), but if I remember correctly, Legends Fisto had a sparring match with post-AotC Kenobi, correct? And during said sparring match, Fisto was the decisive victor. AotC Kenobi was far more developed than TPM Kenobi. TPM Kenobi was virtually Qui-Gon's eaual thanks to the young reader novels which cover Kenobi's training under Qui-Gon. Qui-Gon and Maul were also extremely close, with Maul edging out due to stamina, I believe.
So, Fisto>Post-AotC Kenobi>AotC Kenobi>TPM Kenobi~Qui-Gon<=TPM Maul.
By simple scaling, Fisto>>>TPM Maul.
Of course, looking at Canon, that story changes. We only really have Fisto's accolade from Mace in the Mace Windu comic regarding Fisto being "unrivaled", which, while clearly hyperbole, does let us know that Mace considers Fisto to be top-tier. And we have Fisto's showing against General Griecous, where he easily chops off a hand, scores a hit on Grievous' shoulder, and lands a Force push all in short order. And of course, Fisto blocking a few of Sidious' attacks before dying.
While Maul has many more showings, the only direct line osf comparison between the two seems to be Grievous and Sidious.
Maul has encountered Grievous three times in Son if Dathomir. Once, Grievous seems to easily defeat him. The second battle, Maul tackles Grievous and we don't really see any combat. The third time, Maul Force pushes Grievous without the two ever crossing blades. Maul's showing against Sidious is tricky to count, as Palpatine was clearly toying with the brothers at first, and Maul only really did well after his brother was killed in front of him. And even then, we know Sidious intended to take Maul alive to lure out Talzin, so we know he never actually tried to kill Maul.
Leaving just their performance against Grievous to compare the two in Canon. And on that front, I'd say Kit Fisto did better than Maul, in my opinion. We actually see him crossing blades with the cyborg general for a time, and Grievous never lands so much as a kick on Fisto. The same cannot be said for SoD Maul. And all indication seems to be that SoD Maul>>>TPM Maul, so there's no guarantee TPM Maul could even replicate the level of ability he demonstrated throughout the Clone Wars.