Asajj Ventress vs. Darth Malak

Force, sabers, all out

I'd probably go with Malak, especially if it's SF Malak.

Malak Ventress was losing to savage

Asajj Ventress has better dueling feats. Malak was easily defeated by Revan twice and lost to Mandalore the Ultimate. He only really just outdueled Bastila who was a padawan. Asajj was more overwhelming, stalemating Kenobi and cutting Mace by the knee, also defeanding against Anakin Skywalker. All three of these are superior to Malak as duelists. Malak might be more skilled with the Force, though I am not sure if it is to a degree when he could gain a complete victory over Asajj.
In a saber duel Asajj wins 8/10.
Force battle Malak wins 6-7/10.
All out Asajj might win 6/10.
A good battle, but Ventress is more skilled, faster and more versatile.

Malak should give some degree of difficulty imo. He's physically stronger and could press her at least.