Ventress is arrogence and overconfident.
Maul is skilled and extremely energetic.
Windu is agreesive, yet calm, collective, and very mindful in his duels.
Now considering the fact that Windu has already duelled with Ventress, and held her off well, but Ventress did fair well against Windu. Ventress has a tendancy to flee when she knows she's being bested though, so it's a toughy.
I believe Windu would initially lose, but he'd take Ventress out first and Maul would just about finish him off...