Darth Malak versus Darth Traya
On the surface of Malachor 5 (before its blown up...)
Well lets see what each has going for them...
Malak would try and close the distance seperating himself from Kreia and start wailing on her with his lightsaber. In a one on one lightsaber duel Malak definately has the "edge" (no pun(fun?) intended). However, this advantage would entail that Kreia is not successful in keeping him away from her. Kreia has the advantage in sheer force powers, and would be able to push Malak back and wail on him with force storm. Then again, Malak is also complimented on his strength with the force, and could always retaliate.
I would say Malak, if only because he is younger and "healthier."