Sabres- Probably Maul, although it won't be easy. Zannah was able to briefly fend off an enraged Bane, and held her own against an elite Jedi warrior (trained by the Jedi Weapons Master) who was bigger and stronger than Bane, and was having his powers boosted by battle meditation.
OTOH, Maul is very fast, probably faster than her, and his hand-to-hand skills are almost certainly better. Zannah uses Form 3, so she'd last quite a while, but Maul, with his speed, h-t-h skills and Juyo mastery could well get through.
Force- Zannah. She was able to cloak herself with a fake aura of light-side power and stroll right into the Jedi archives with no-one realising what she really was. She also 'cloaked' both herself and Bane to hide from a Jedi search party, and was able to drive people insane by making them see terrifying hallucinations.
All-out- not sure. Zannah would probably go for the mind-****, but Maul might be able to resist it. Even then she could well be able to land a killing blow. It really could go either way I think.
Not to mention a telepath was rendered catatonic while trying to read Maul's mind, suggesting that his psychic defences are very strong. Also, while he's not as tall or strong as Sarro, he's almost certainly faster.
I see the fight going something like this:
Zannah attempts to use Sith sorcery. Maul resists it and dispells the illusions. Zannah attacks while he's still distracted but he evades it. Zannah switches to defensive strategy as Maul attacks.
She fends off Maul's attacks for a good while but eventually he lands something like, say, a kick to the back of her knee. This throws off her balance and her defence falters enough for Maul to get through and land the killing blow.
I wouldn't rule Zannah out completely, but yeah, most likely Maul.