Ahsoka in a seriously close fight. They're both very impressive combatants, but I see Maul faltering, seeing as Maul has been isolated and it's reasonable to assume he's been out of practice for a very long time, where Ahsoka has been in combat far more frequently. SoD Maul would have dispatched the Inquisitiors alone far faster than his current incarnation did, even while being helped.
Maul's loss to Kanan was not due to his nonexistent 'superiority' but to Maul being who he is. He was overconfident, seeing Kanan as someone who would be easily discarded, seeing as he is already inferior in lightsaber combat, Force prowess, and he was blind. He had every reason to believe Kanan would be an easy kill; however, he didn't anticipate Kanan being able to put up any fight, and this made a noticeably reckless attack meant to bisect him which was easily countered by Kanan who was using the Force to sense his surroundings, giving him heightened awareness and improved premonition. In a drawn out duel where they were on equal footing with no prior injuries (namely Maul's surprise attack that blinded Kanan), Maul would slaughter him. It's pretty much the same thing that got him bisected by Kenobi in TPM, only it was his overconfidence rather than being completely off-guard.